Lower Unit Drain Gasket – Fits Yamaha Marine Engines (Replaces 90430-08003-00)
Lower Unit Drain Gasket – Fits Yamaha Marine Engines (Replaces 90430-08003-00) 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 Unit Drain Gasket – Fits Yamaha Marine Engines (Replaces 9043...
Product Details
This is a high-quality aftermarket Yamaha Outboard Lower Unit Drain Gasket designed for a universal fit across all Yamaha Marine 2-stroke and 4-stroke outboard engines from 1985 to the current model year. It creates a critical seal for both the drain and vent plugs, preventing water intrusion and gear lube leaks.
It serves as a direct replacement for Yamaha part numbers 90430-08003-00, 90430-08020-00, 90430-08801-00, 604-45342-00-00, and Sierra 18-4698.
- Installs between the drain/vent plug and the lower unit housing.
- Made from a durable black rubber compound, which supersedes the older reddish-orange material.
- Essential for routine lower unit maintenance and gear lube changes.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 90430-08003-00 |
| Yamaha | 90430-08020-00 |
| Yamaha | 90430-08801-00 |
| Yamaha | 604-45342-00-00 |
| Sierra | 18-4698 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | All Outboard Models | 2–350 | 2-Stroke & 4-Stroke | 1985–Current | 90430-08003-00 | Used on both drain and vent plugs; supersedes 90430-08020-00 |
Technical Specs
- Product Type
- Lower Unit Drain Gasket
- Installation
- Placed between drain plug and lower unit housing
- Housing Material
- Black rubber compound (replaces older reddish-orange material)
- Housing Color
- Black
- Dimensions
- Ring-shaped: Approx. 14-16mm outer diameter
- Weight
- < 0.01 kg (< 0.32 oz)
- Fitting Type
- Sealing gasket
- Thread Size
- Compatible with lower unit drain plug threads
- Operating Temperature
- -30°C to 120°C (estimated operating range)
- Warranty
- Manufacturer warranty applies
- Other Technical Attributes
- Used for both drain plug and vent plug locations
What’s in the Box
- 1 x Drain Plug Gasket (90430-08003-00)
Note: Yamaha recommends purchasing two gaskets when servicing an outboard, as this gasket is used for both the drain plug and vent plug locations.
Installation Notes
- Position a suitable drain pan underneath the lower unit.
- Remove both the lower drain plug and the upper vent plug to allow the oil to drain properly.
- Inspect the magnetic tip of the drain plug for any metal shavings, which can indicate gear wear.
- Remove and discard the old gaskets from both plugs. Never reuse gaskets.
- Clean the plug and housing surfaces where the gasket will sit.
- Install a new gasket onto both the drain plug and the vent plug.
- Fill the lower unit with manufacturer-specified gear lube through the bottom drain hole until fluid begins to seep out of the upper vent hole.
- Install the upper vent plug first, then install the bottom drain plug to create a vacuum and minimize fluid loss.
- Tighten both plugs to be snug. Do not overtighten, as this can damage the gasket or threads.
- Wipe the area clean and check for any leaks after a short period.
Troubleshooting & FAQ
How many gaskets do I need for a gear lube change?
You need two gaskets. Yamaha outboards use one gasket for the lower magnetic drain plug and a second identical gasket for the upper oil-level vent plug. It is critical to replace both during service.
Is this gasket reusable?
No. These are single-use crush gaskets. Reusing an old gasket will likely result in a poor seal, leading to water intrusion into your gearcase and expensive damage.
What are signs of a failing gasket?
Common signs include visible gear lube leaking from the drain or vent plugs, or discovering milky, emulsified gear lube during a change, which indicates water has entered the lower unit.
Why is this gasket black instead of the old reddish-orange color?
Yamaha updated the material from the original reddish-orange fiber/rubber compound to a more durable black rubber. This black gasket is the direct OEM-specified replacement and offers improved sealing properties.
How often should I change these gaskets?
You should replace these gaskets every time you change your lower unit gear lube, which is typically recommended annually or every 100 hours of operation, whichever comes first.
What is the difference between OEM and this aftermarket part?
This listing is an aftermarket replacement, not an OEM component. It has been engineered to meet or exceed original equipment manufacturer (OEM) specifications for fit, form, and function, using comparable materials. Our parts are made in an ISO 9002 certified facility and are batch-inspected for quality assurance.
What are the shipping speed and cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free for most orders, with expedited options available at checkout where applicable.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. Should any issues arise, contact our support team with your order details for assistance. Returns are accepted within our standard window for unused items in their original condition. Please see our full policy page or contact us 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.
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