Lower Unit Oil Drain Plug Gasket – Yamaha Outboard Replacement for 90430-08003 and 90430-08020

Product Details

This aftermarket lower unit oil drain plug gasket is designed to replace the sealing washer used with specified Yamaha outboard gearcase drain plugs. A new gasket helps restore a dependable seal during lower unit gear-oil service and helps reduce the risk of oil seepage at the drain plug.

Catalog references identify this gasket with Yamaha OEM numbers 90430-08003-00 and 90430-08020-00. The same replacement family is also cross-referenced to Sierra 18-4698 and 18-46981-9, and to Mercury Marine 27-81987 and 27-81987M. These references are provided for identification and comparison; always confirm the exact application for your engine before installation.

• Replacement sealing gasket for a compatible lower unit oil drain plug.
• Suitable for routine gear-oil service when the original gasket is worn, compressed, or damaged.
• Sold as one gasket.
• Aftermarket replacement; not an OEM-branded Yamaha or Mercury component.

Part Number Matrix

Use the following documented manufacturer and aftermarket references to compare the replacement gasket with the part currently installed on your outboard.

Engine & Model Compatibility

This gasket is associated in the referenced catalogs with Yamaha outboard lower-unit applications using OEM gasket numbers 90430-08003-00 or 90430-08020-00. The available evidence does not establish one universal horsepower, stroke, model-year, shaft-length, or serial-number range.

Because lower-unit components can vary by model, year, gearcase, and serial-number range, do not rely on horsepower alone. Confirm the OEM number in your engine parts diagram or compare the original gasket and drain-plug application before ordering.

Technical Specs

Product Type

Lower Unit Oil Drain Plug Gasket

Quantity

1 gasket

Material

Not specified in the available product records

Color

Not specified

Thread or Plug Size

Use only with the compatible drain-plug application; verify against the engine parts diagram

Brand Status

Aftermarket replacement

What’s in the Box

• 1 x Lower unit oil drain plug gasket

Installation Notes

1. Place a suitable drain pan beneath the lower unit and follow the procedure in your outboard service or owner’s manual.
2. Remove the lower unit oil drain plug and retain the drained gear oil for inspection or dispose of it according to local requirements.
3. Remove the old gasket and clean the drain-plug threads and the sealing surface on the gearcase.
4. Inspect the drain plug and its sealing surface for damage, corrosion, or damaged threads.
5. Install the new gasket on the compatible drain plug.
6. Refit and tighten the drain plug using the torque specification and service procedure for your exact engine. Do not use an unverified torque value.
7. Refill the lower unit with the specified gear lubricant according to the manufacturer’s procedure.
8. Check the drain-plug area for leakage after servicing and again after the engine has been operated.

Troubleshooting & FAQ

Safety & Important Info

• Verify the OEM reference and exact engine application before purchasing.
• Do not assume fitment from horsepower, stroke type, or brand alone.
• Use the torque specification and lubricant specified for your exact outboard model.
• Inspect for leaks after installation. Continued leakage may cause water contamination or gearcase damage.
• This is an aftermarket replacement and is not manufactured or endorsed by Yamaha or Mercury Marine.

About Sea Sierra

• Marine Replacement Parts — We supply replacement components for outboard and marine service applications.
• Reference-Based Ordering — Manufacturer and aftermarket reference numbers are provided to help customers compare parts before purchase.
• Service-Focused Information — Product details are presented to support careful identification and installation using the appropriate engine documentation.