Lower Gearcase Oil Drain Gasket – Fits Yamaha Outboard Motors (Replaces 90430-08003-00, 90430-08020-00)
Lower Gearcase Oil Drain Gasket – Fits Yamaha Outboard Motors (Replaces 90430-08003-00, 90430-08020-00) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Lower Gearcase Oil Drain Gasket – Fits Yamaha Outboard Motors (Repl...
Product Details
This Lower Gearcase Oil Drain Gasket provides a secure, leak-free seal for the lower unit drain and fill plugs on virtually all Yamaha outboard motors from 1984 to the present (2.5HP to 350HP, 2-stroke and 4-stroke models). It is a small but critical component that prevents gear oil leaks, ensuring proper lubrication and protecting the internal components of your outboard's lower unit from water intrusion and corrosion.
This part offers a direct replacement for Yamaha part numbers 90430-08020-00, 90430-08003-00, 90430-08021-00, 90430-08801-00, Sierra 18-4698, and 604-45342-00-00.
- Engineered for marine environments; made from a durable fiber/composite material resistant to oil, fuel, and saltwater.
- Designed as a single-use crush washer; should be replaced with every gear oil change to guarantee a perfect seal.
- Typically, two gaskets are required per outboard service: one for the drain plug and one for the upper fill/vent plug.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 90430-08020-00 |
| Yamaha | 90430-08003-00 |
| Yamaha | 90430-08021-00 |
| Yamaha | 90430-08801-00 |
| Yamaha | 604-45342-00-00 |
| Sierra | 18-4698 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This gasket has a universal fit across the Yamaha outboard lineup.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | All Outboards | 2.5–350 | 2- & 4-Stroke | 1984–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
Technical Specs
- Product Type
- Lower Unit Drain Gasket
- Installation
- Replace with each oil change
- Connection
- 3/8"-16 Drain/Fill Screw
- Housing Material
- Fiber/Composite
- Housing Color
- Red/Orange
- Dimensions
- Small crush washer
- Weight
- <1 oz (<28g)
- Fitting Type
- Crush washer/gasket
- Thread Size
- 3/8"-16
- Other Technical Attributes
- Marine-grade material resistant to oil and saltwater
What’s in the Box
- 1 x Drain Gasket (Replaces 90430-08003-00 / 90430-08020-00)
- Note: This part is also available in multi-packs for convenience.
Installation Notes
- Position a suitable drain pan under the lower unit of your outboard.
- Remove the lower drain screw, followed by the upper fill/vent screw to allow oil to drain completely.
- Inspect the magnetic tip of the drain screw for any metal shavings, which can indicate gear wear.
- Remove and discard the old gaskets from both the drain and fill screws.
- Clean the screw threads and the sealing surfaces on the lower unit to ensure they are free of old gasket material, dirt, and oil.
- Place the new gasket onto the drain screw and reinstall it, tightening to the manufacturer's specified torque. Do not overtighten.
- Fill the gearcase with the recommended gear lubricant through the upper fill hole until oil begins to weep out.
- Install the new gasket on the upper fill screw and tighten it securely.
- Wipe the area clean and check for any leaks after a brief engine run on a flusher.
Troubleshooting & FAQ
How often should this gasket be replaced?
For a guaranteed leak-proof seal, you should use a new gasket every time you change your lower unit gear oil. Reusing old gaskets can lead to leaks and water intrusion.
How many gaskets do I need for one engine service?
Typically, you will need two gaskets: one for the lower magnetic drain plug and one for the upper oil level/fill plug.
What are the signs of a failing drain plug gasket?
Common signs include visible gear oil dripping from the drain plug area or a milky, cloudy appearance in your gear oil, which indicates water has contaminated the system through a failed seal.
Will this fit my Mercury, Johnson, or other brand outboard?
No. This part is specifically designed to meet the dimensions and material requirements for Yamaha outboards. Using it on other brands may result in an improper seal.
Is this crush washer reusable?
No. It is a single-use crush washer designed to deform slightly upon tightening to create a perfect seal. Once compressed, it will not provide a reliable seal if used again.
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
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