Gearcase Seal Kit – Fits Mercury/Mariner 175-300HP V6/V8 Outboards (Replaces 8M0142979)

Gearcase Seal Kit – Fits Mercury/Mariner 175-300HP V6/V8 Outboards (Replaces 8M0142979)

This gearcase seal kit is designed for Mercury Marine 175-300HP 3.4L V6 and 4.6L V8 PRO XS / Verado outboard engines. It provides the necessary components to reseal the lower unit, preventing water intrusion and oil leaks.

This kit serves as a direct replacement for multiple OEM and aftermarket part numbers, ensuring a precise fit and reliable performance for a wide range of compatible engine models.

• Installation: Direct OEM-spec replacement.
• Function: Seals the gearcase to protect internal components from water and contaminants.
• Weight: 0.57 lbs (0.26 kg).

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.

Technical Specifications

Installation Guide

1. Drain the gearcase lubricant completely by removing the drain and vent screws.
2. Remove the propeller and any associated hardware.
3. Unbolt and carefully separate the lower unit (gearcase) from the outboard's midsection.
4. Disassemble the gearcase components as required to access the propeller shaft and driveshaft seals.
5. Carefully extract all old seals and O-rings from their housings, taking care not to scratch the sealing surfaces.
6. Thoroughly clean all components and sealing surfaces of old sealant, oil, and debris.
7. Lubricate the new seals with marine grease and press them into place using a suitable seal driver or socket.
8. Reassemble the gearcase, ensuring all components are installed correctly and bolts are torqued to manufacturer specifications.
9. Re-install the lower unit onto the engine.
10. Refill the gearcase with the manufacturer-recommended lubricant to the proper level.

Troubleshooting & FAQ

How do I confirm this seal kit fits my Mercury engine?
Verify your engine's model and horsepower rating against the "Compatible Engine Models" table. For V8 Racing models, it is critical to confirm your serial number is 1E080500 or newer, and for AMS Racing models, 1E081459 or newer. Always cross-reference the OEM part number, 8M0142979 or 26-8M0142979, with your engine's service manual to ensure an exact match.

What are the common signs that my gearcase seals are failing?
The most common sign is milky or water-contaminated gear lube when you drain it. Other symptoms include visible oil leaking from the propeller shaft area or a persistent sheen of oil on the water around your lower unit after it has been sitting.

Is any special tool required for installation?
While basic hand tools are sufficient for disassembly, using a dedicated seal puller and a proper seal driver (or a socket of the exact correct diameter) is highly recommended. This ensures the old seals are removed and new seals are installed without damaging the seal or its housing, preventing future leaks.

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.