Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner/Force 30-125 HP Outboards (Replaces 26-43035A4, 18-2626)

Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner/Force 30-125 HP Outboards

This lower unit gearcase seal kit contains the necessary components to rebuild the gearcase for a wide range of Mercury, Mariner, and Force outboards. It is designed to fit models from 30 HP to 125 HP, covering both 2-stroke and 4-stroke engines from 1983 to the present.

This kit is a direct replacement for multiple OEM and aftermarket part numbers, ensuring a precise fit for compatible models. It is specifically designed for lower units with a 4.25" (107.95mm) gearcase diameter.

• Installation: Direct replacement design for straightforward installation.
• Compatibility: Fits Mercury/Mariner 30–125 HP (1983-current) and Force 75–120 HP (1995–1999) outboards.
• Complete Kit: Includes a comprehensive set of seals, gaskets, and O-rings for a full gearcase service.

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 Force models, confirm your engine model/year in the table below.

Mercury/Mariner Applications

Force Applications

Technical Specifications

Package Contents

The kit includes the following components to service your lower unit:

• 1 x Water Line Seal
• 1 x Drain Screw Gasket
• 1 x Impeller Gasket
• 1 x Washer
• 1 x Insulator Bushing
• 1 x O-Ring
• 1 x Oil Seal
• 1 x Drive Shaft Oil Seal

Note: The exact contents may vary slightly between brands, but all kits include the necessary seals and gaskets for a complete gearcase rebuild.

Installation Guide

Professional installation is recommended. The following is a general guide:

1. Drain the gearcase oil by removing the lower and upper drain/vent screws.
2. Carefully remove the propeller assembly.
3. Unbolt and detach the lower unit (gearcase) from the outboard's midsection.
4. Disassemble the gearcase components, including the bearing carrier and driveshaft, to access the old seals.
5. Remove all old seals, O-rings, and gaskets, taking care not to scratch any sealing surfaces.
6. Thoroughly clean all mating surfaces, removing any old sealant or corrosion.
7. Lubricate the new seals with a light coat of marine grease and install them into their respective bores, ensuring they are seated properly.
8. Install the new O-rings and gaskets during reassembly.
9. Reassemble the gearcase components according to the manufacturer's torque specifications.
10. Reinstall the lower unit onto the outboard.
11. Refill the gearcase with the recommended marine gear lubricant until it flows from the upper vent hole.
12. Reinstall both drain/vent screws with new gaskets and check for any leaks after a short period.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my engine?

A: The best way to confirm fitment is to check your engine's model, year, and serial number against the "Compatible Engine Models" table. This kit is specifically for Mercury, Mariner, and Force outboards with a 4.25" (107.95mm) gearcase diameter. You can also match your existing part number with our "Part Number Cross-Reference" list.

Q: What are the signs that my gearcase seals need replacing?

A: Common signs of failing gearcase seals include milky, water-contaminated gear oil (which looks like coffee with cream), visible oil leaks around the propeller shaft or driveshaft area, or a persistent fishy, burnt oil smell. A pressure test of the lower unit can also confirm a leak.

Q: How often should I replace the gearcase seals?

A: We recommend inspecting your gear lube at every service interval (or at least annually). You should replace the seals as a preventative measure whenever the lower unit is removed for other service (like a water pump impeller change) or immediately if you detect any signs of leakage or water intrusion.

Q: OEM vs. Aftermarket?

A: 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.

Q: How fast do you ship and how much does it cost?

A: 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.

Q: What is your warranty and return policy?

A: 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.