26-816575A6 Gear Housing Seal Kit for Mercury 2.5XS 225XS 250XS 250XB 300X 300XS | JLM Marine

Gear Housing Seal Kit – Fits Mercury 2.5XS, 225XS, 250XS, 250XB, 300X, 300XS Outboards

This Gear Housing Seal Kit is engineered to fit a wide range of Mercury high-performance outboard engines, including the 2.5XS DFI, 225 PRO XS, 250 PRO XS, 250 Sport XS, 250XB, 300X PRO MAX, 300 SuperMagnum, and 300XS models. Designed to restore proper sealing in your lower unit, this kit ensures reliable protection against water intrusion and maintains optimal gearcase performance.

This kit directly replaces Mercury OEM part number 26-816575A6, providing a precise fit for engines ranging from 2.5L to 3.2L displacement across DFI and EFI fuel systems.

• Includes all seals and components shown in product images for complete lower unit service
• Compatible with both DFI (Direct Fuel Injection) and EFI (Electronic Fuel Injection) Mercury outboards
• Designed for high-performance XS and PRO XS series engines

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

Package Contents

This kit includes:

• 1 × Gear Housing Seal Kit (all seals and components as shown in product images)

Installation Guide

1. Disconnect the battery and remove the outboard from the boat or tilt it fully to access the lower unit. Drain all gear oil from the gearcase before disassembly.
2. Remove the propeller, then unbolt the lower unit from the mid-section. Carefully separate the gear housing and note the positions of all shims and washers.
3. Remove the old seals from the gear housing, propeller shaft, and drive shaft locations. Clean all seal surfaces thoroughly, removing any old gasket material or corrosion.
4. Inspect all seal grooves and mating surfaces for damage or wear. Replace any damaged components as necessary.
5. Lubricate new seals with marine-grade grease or gear oil before installation. Install each seal carefully, ensuring proper orientation and seating depth.
6. Install the propeller shaft seal, ensuring the lip faces inward toward the gear oil. Tap gently with a seal driver to seat it evenly.
7. Install the drive shaft seals and O-rings in their respective grooves, checking for smooth fitment without pinching.
8. Reassemble the gear housing components in reverse order, reinstalling all shims and spacers in their original positions.
9. Reattach the lower unit to the mid-section, torquing mounting bolts to manufacturer specifications. Ensure proper alignment of the drive shaft splines.
10. Refill the gearcase with the correct grade and quantity of Mercury gear oil through the lower fill hole until it reaches the upper vent hole.
11. Install and tighten both drain plugs with new sealing washers. Reinstall the propeller and torque the propeller nut to specification.
12. Test run the engine in a tank or on the water, checking for leaks around all seal locations. Monitor gear oil level after the first hour of operation.

Troubleshooting & FAQ

Q: How do I confirm this seal kit fits my specific Mercury engine?
A: Cross-reference your engine model and serial number with the compatibility table above. You can find your engine's serial number on the mounting bracket or use our Mercury Serial Number Guide to identify your model year and displacement.

Q: What are the signs that my gear housing seals need replacement?
A: Common symptoms include milky or contaminated gear oil (indicating water intrusion), oil leaking from the lower unit, unusual noise or vibration from the gearcase, or difficulty shifting. Regular gear oil inspection every 50–100 hours can help catch seal failure early.

Q: How often should I replace the gear housing seals?
A: Mercury recommends inspecting seals during every lower unit service (typically every 100 hours or annually). Replace seals if you notice any leakage, during gearcase overhaul, or anytime the lower unit is disassembled for service or repair.

Q: Can I install this seal kit myself, or do I need a marine technician?
A: Lower unit seal replacement requires mechanical skill, specialized tools (seal drivers, torque wrench), and knowledge of proper shimming and alignment procedures. If you lack experience with outboard lower unit service, professional installation is strongly recommended to avoid costly damage.

Q: Does this kit include all the seals needed for a complete lower unit rebuild?
A: This kit includes the seals shown in the product images as specified by Mercury part number 26-816575A6. For a complete rebuild, you may need additional components such as bearings, gaskets, or shift shaft seals depending on your engine's condition—consult your service manual.

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.