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)

This gasket provides a secure, leak-free seal for the lower unit drain and fill plugs on Yamaha outboard motors. Replacing it during each gear oil change prevents lubricant leaks, ensuring the lower unit's gears are properly lubricated and protected from water intrusion and corrosion.

Designed for universal compatibility, this gasket fits all Yamaha 2-stroke and 4-stroke outboard models from 2.5 HP to 350 HP, manufactured between 1984 and the present. It serves as a direct replacement for multiple OEM part numbers.

• Installation: Should be replaced with every gear oil change to ensure a proper seal.
• Function: Creates a tight seal for the 3/8"-16 drain/fill screw, preventing oil leaks.
• Material: Constructed from a durable, marine-grade fiber/composite material resistant to oil and saltwater.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Technical Specifications

Package Contents

1 x Gasket (Replaces 90430-08003-00 / 90430-08020-00)

Note: Multiple quantity packages are available. Options include 3-packs, 6-packs, 10-packs, 15-packs, 20-packs, and 30-packs.

Installation Guide

1. Place a drain pan under the lower unit's gearcase.
2. Using a large flathead screwdriver or appropriate socket, remove the lower drain/fill plug.
3. Remove the upper vent plug to allow air to enter and oil to drain smoothly.
4. Allow the gear oil to drain completely. Inspect the oil for any metallic shavings or milky appearance, which could indicate gear wear or water intrusion.
5. Clean the magnetic tip of both plugs and discard the old gaskets.
6. Install a new gasket onto the lower drain/fill plug.
7. Reinstall the lower drain/fill plug and tighten it snugly. Do not overtighten.
8. Insert your gear lube pump into the lower drain hole and pump new gear oil in until it flows out of the upper vent hole.
9. Install a new gasket on the upper vent plug.
10. Reinstall the upper vent plug securely BEFORE removing the lube pump from the lower hole to prevent oil loss.
11. Quickly remove the lube pump and reinstall the lower drain/fill plug.
12. Wipe the area clean and check for any leaks around the plugs after a few minutes.

Troubleshooting & FAQ

How do I confirm this gasket fits my engine?
This gasket has a universal fit for all Yamaha outboard models (2.5HP-350HP, 2-stroke and 4-stroke) from 1984 to present. You can verify the part number using the cross-reference table provided.

How often should I replace this gasket?
It is critical to replace this gasket every time you change your gearcase oil. This ensures a fresh, reliable seal and prevents damaging oil or water leaks.

How many gaskets do I need for a complete service?
Typically, two gaskets are required per outboard. One is for the lower drain plug, and the second is for the upper oil level/vent plug.

What are the signs of a failing drain plug gasket?
The most common sign is a visible gear oil leak around the lower unit drain or vent plugs. If left unaddressed, this can lead to low oil levels and severe gearcase damage.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.