Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces Yamaha 90430-08003-00, 90430-08020-00, Mercury 27-81987)
Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces Yamaha 90430-08003-00, 90430-08020-00, Mercury 27-81987) is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces ...
Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces Yamaha 90430-08003-00, 90430-08020-00, Mercury 27-81987) is backordered and will ship as soon as it is back in stock.
Product Details
This fiber/composite Yamaha Outboard Lower Unit Drain Gasket creates a secure, leak-free seal for the lower unit drain and vent plugs. It is designed for a wide range of Yamaha 4-Stroke Outboard Motors, from 2.5 HP to 350 HP, manufactured from 1998 to the present.
It serves as a direct replacement for Yamaha part numbers 90430-08003-00 and 90430-08020-00, as well as aftermarket equivalents like Sierra 18-0826 and Mercury 27-81987.
- Installs with basic hand tools.
- Functions as a compression crush washer for a tight seal.
- This is the newer black composite style that supersedes the earlier reddish-orange version.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 90430-08003-00 | Current OEM part. Supersedes 90430-08020-00. |
| Yamaha | 90430-08020-00 | Earlier reddish-orange part, superseded by 90430-08003-00. |
| Sierra | 18-0826 | Direct aftermarket cross-reference. |
| Mercury | 27-81987 | Interchangeable aftermarket part. |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This gasket fits nearly all Yamaha 4-stroke outboards from 2.5 to 350 HP manufactured between 1998 and today.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F2.5 | 2.5 | 4-Stroke | 2003–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F4 | 4 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F6 | 6 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F8 | 8 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F9.9 | 9.9 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F15 | 15 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F20 | 20 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F25 | 25 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F30 | 30 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F40 | 40 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F50 | 50 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F60 | 60 | 4-Stroke | 2002–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F70 | 70 | 4-Stroke | 2010–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F75 | 75 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F80 | 80 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F90 | 90 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F100 | 100 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F115 | 115 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F150 | 150 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F175 | 175 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F200 | 200 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F225 | 225 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F250 | 250 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F300 | 300 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F350 | 350 | 4-Stroke | 2008–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
Technical Specs
- Product Type
- Lower Unit Drain Gasket
- Installation
- Manual (hand tools)
- Connection
- Compression washer
- Housing Material
- Fiber/Composite
- Housing Color
- Black (newer style); earlier versions were reddish-orange
- Dimensions
- Approx. 19 mm OD
- Weight
- <5g
- Fitting Type
- Crush washer
- Thread Size
- Compatible with M8 drain plugs
- Other Attributes
- Supersedes earlier reddish-orange gasket (90430-08020-00)
What’s in the Box
- 1 x Gasket (Replaces 90430-08003-00)
Note: This gasket is used on both the vent and drain plug. For a complete lower unit oil change, order quantity two.
Installation Notes
- Position a drain pan under the lower unit.
- Remove both the lower drain plug and the upper vent plug screws.
- Allow the gear oil to drain completely. Inspect the old oil for a milky appearance (water) or metal filings.
- Clean the plug sealing surfaces on the gearcase.
- Remove and discard the old gaskets from both plugs. Never reuse them.
- Install a new gasket on each plug.
- Inject the recommended gear lube into the bottom drain hole until fluid flows from the upper vent hole.
- Install the upper vent plug with its new gasket first. Tighten securely.
- Quickly remove the lube filler tube and install the lower drain plug.
- Tighten the drain plug to the manufacturer's specified torque. Do not overtighten.
- Wipe the area clean and check for any leaks after a few minutes.
Troubleshooting & FAQ
How do I know if this gasket is overtightened?
Over-tightening can crush the gasket and cause a leak. Always tighten plugs to the manufacturer's specified torque using a torque wrench. If one is not available, tighten until snug, then turn an additional 1/4 turn. The gasket should feel compressed but not distorted.
The new black gasket feels harder than my old red one. Is this correct?
Yes. The current Yamaha OEM part (90430-08003-00) is a black, harder composite material that supersedes the older, reddish-orange gasket (90430-08020-00). While some users note a difference in feel, this is the correct updated part for the specified models.
How often should I replace these gaskets?
It is critical to use a new gasket every time you change your lower unit gear oil. Reusing old, crushed gaskets is a primary cause of leaks and potential water intrusion, which can lead to catastrophic gearcase failure.
What are the signs of a failed drain plug gasket?
The most common sign is a slow drip of gear oil from the drain or vent plug. Another key indicator is milky or creamy-looking oil during a fluid change, which signals water has entered the lower unit through a failed seal.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
