Lower Unit Drain Plug Screw & Gasket Kit for Yamaha, Nissan/Tohatsu and Mercury/Mariner Outboards

Product Details

This Lower Unit Drain Plug Screw & Gasket Kit is a replacement service set for lower-unit oil drain applications on selected Yamaha, Nissan/Tohatsu, and Mercury/Mariner marine outboards. It combines a drain plug screw with a replacement sealing gasket for routine gear-oil service.

Fitment is determined by the original plug and gasket specification, not by horsepower alone. Compare your existing part and the reference numbers below before ordering. Model, year, shaft length, serial number, and lower-unit configuration may affect compatibility.

• Replacement lower-unit oil drain plug and sealing gasket
• Suitable for service and replacement of worn or damaged drain hardware
• Aftermarket replacement supplied under the listed aftermarket reference
• Verify the original part number, plug style, thread, and sealing surface before installation

Part Number Matrix

The following manufacturer and aftermarket references are listed for this product. These numbers are reference identifiers; always confirm that the original plug and gasket match before purchase.

Engine & Model Compatibility

This kit is listed for selected Yamaha, Nissan/Tohatsu, and Mercury/Mariner outboard lower-unit drain applications. The available product data does not establish one universal horsepower, model-year, stroke, shaft-length, or serial-number range. Confirm the complete fitment condition by matching the original reference number and physical plug configuration.

Technical Specs

Product type

Lower-unit drain plug screw and gasket kit

Application

Outboard lower-unit gear-oil drain service

Included sealing component

Replacement gasket included

Brand coverage

Selected Yamaha, Nissan/Tohatsu, and Mercury/Mariner applications

Aftermarket reference

Sierra Marine 18-2371

Fitment method

Match the original part number and physical configuration; do not rely on horsepower alone

What's in the Box

• 1 × Lower-unit drain plug screw
• 1 × Lower-unit oil drain gasket

Installation Notes

1. Place the boat on a stable, level surface and follow the engine manufacturer's service procedure.
2. Allow the lower unit to cool before beginning service.
3. Remove the existing drain plug and inspect the threads and sealing surface.
4. Clean the plug opening and surrounding sealing area, keeping debris out of the lower unit.
5. Install the supplied gasket with the replacement drain plug.
6. Start the plug by hand to prevent cross-threading.
7. Tighten to the torque specified in the applicable engine service manual. Do not over-tighten.
8. After refilling the lower unit with the correct gear oil, inspect the drain plug area for leakage.

Troubleshooting & FAQ

How do I verify that this kit fits?

Match your original drain plug and gasket to the listed manufacturer reference numbers. Check the plug style, thread, sealing surface, and lower-unit configuration. Horsepower by itself is not sufficient to confirm fitment.

Does the kit include the gasket?

Yes. The kit includes one replacement drain plug screw and one replacement lower-unit oil drain gasket.

Can I reuse the old gasket?

A drain-plug gasket should normally be replaced during lower-unit oil service. Reusing a compressed or damaged gasket can cause seepage.

What torque specification should I use?

Use the exact torque value specified in the service manual for your engine and lower-unit model. Do not use a generic torque value because specifications can vary.

Is the plug magnetic?

Magnetic features are not specified for this product. Confirm whether your original plug is magnetic before ordering if that feature is required for your application.

Is this an OEM part?

This is an aftermarket replacement. Sierra Marine reference 18-2371 is listed for this product. Manufacturer names and part numbers are used only to identify compatible reference applications.

When should the gasket be replaced?

Replace the gasket whenever the lower-unit oil is serviced, or sooner if you notice oil seepage, a damaged sealing surface, or a worn plug.

Safety & Important Information

• Confirm the part number and physical configuration before ordering.
• Keep the model, year, stroke, shaft, and serial-number conditions together when checking fitment.
• Do not force a plug that does not start smoothly by hand.
• Use the correct gear oil and follow the engine manufacturer's service procedure.
• This is an aftermarket replacement, not an OEM component.

About Sea Sierra

• Marine replacement parts selected for routine service and repair applications.
• Product references are provided to help customers compare their original parts before ordering.
• Support is available for fitment questions when the engine model and original part information are provided.