Lower Unit Gasket Seal Kit - Fits Mercury/Mariner 25-30HP Outboards (Replaces 27-8M0089639, 95220A1)

Lower Unit Gasket Seal Kit – Fits Mercury/Mariner 25-30HP Outboards (Replaces 27-8M0089639, 95220A1)

This lower unit gasket and seal kit is designed for Mercury/Mariner 2-stroke, 25-30HP and 25 Jet HP outboard engines manufactured between 1984 and 1991.

It serves as an aftermarket replacement for Mercury part numbers 27-8M0089639, 95220A1, 804908A01, and 27-8M0089636.

• Designed for installation in the lower unit/gear case assembly.
• Includes all standard seals, gaskets, and O-rings needed for a lower unit overhaul.
• Cross-referenced with both Mercury/Mariner and Yamaha part numbers for broad compatibility.

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 Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

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

This kit includes all necessary gaskets, seals, and O-rings required for a complete lower unit/gear case service. Replaces OEM part number kits 27-8M0089639, 95220A1, 804908A01, and 27-8M0089636.

Installation Guide

Professional installation is recommended. The general steps are outlined below:

1. Drain Oil: Drain the gearcase oil completely by removing the drain and vent plugs.
2. Remove Propeller: Remove the cotter pin, propeller nut, and propeller from the propeller shaft.
3. Detach Lower Unit: Unbolt and carefully slide the lower unit away from the outboard's upper housing.
4. Disassemble: Disassemble the lower unit components, including the water pump assembly, bearing carriers, and driveshaft. Keep track of all hardware.
5. Remove Old Seals: Carefully remove all old gaskets, seals, and O-rings from their housings.
6. Clean Surfaces: Thoroughly clean all mating surfaces, ensuring they are free of old gasket material, corrosion, and debris.
7. Install New Components: Install the new seals and O-rings, applying a light coat of marine grease to the sealing lips. Place the new gaskets onto the prepared surfaces.
8. Reassemble: Reassemble the lower unit components in the reverse order of disassembly.
9. Torque Bolts: Tighten all bolts to the manufacturer's specified torque values to prevent leaks and ensure proper alignment.
10. Reinstall Unit: Reattach the lower unit to the outboard and reinstall the propeller assembly.
11. Refill Lubricant: Fill the gearcase with the recommended lower unit lubricant until it flows from the upper vent hole, then install both plugs.
12. Final Check: After a short run, check for any signs of oil or water leaks around the seals.

Troubleshooting & FAQ

How do I confirm this kit fits my specific engine model?

This kit fits a range of Mercury/Mariner 25-30HP 2-stroke outboards from 1984-1991. Please check the 'Compatible Engine Models' table on this page and cross-reference your engine's model or serial number. For further verification, consult the linked Mercury serial number guide or compare your existing part numbers to our cross-reference list.

What are the signs that my lower unit gasket kit needs replacement?

Common signs of a failing lower unit seal include milky or creamy-looking gear lube (indicating water intrusion), visible oil leaks around the propeller shaft or driveshaft, or a metallic sheen in the oil caused by bearing wear. Regular inspection during oil changes is the best way to catch these issues early.

Does this kit include everything I need for the job?

This kit contains all the standard gaskets, seals, and O-rings for a lower unit service. However, you will still need appropriate hand tools, a torque wrench, marine grease, and fresh gearcase lubricant to complete the installation.

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.