Gearcase Seal Kit – Fits Mercury/Mariner 175-300HP V6/V8 (Replaces 8M0142979, 26-8M0142979)

$72.59

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This aftermarket Gearcase Seal Kit is designed for Mercury/Mariner 175-300HP V6 3.4L & V8 4.6L 4-Stroke engines, including Pro XS and Verado models with serial numbers 2B529482 and up.

It serves as a direct replacement for Mercury Marine part numbers 8M0142979 and 26-8M0142979, and interchanges with WSM 26-8M0142979 and GLM Marine 87532.

Engineered for direct OEM replacement fit and function.
Includes all necessary seals and O-rings for a standard lower unit service.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury Marine	8M0142979
Mercury	26-8M0142979
WSM	26-8M0142979
GLM Marine	87532

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Mercury/Mariner	V6 3.4L	175	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V6 3.4L	200	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V6 3.4L	225	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V8 4.6L	200	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V8 4.6L	225	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V8 4.6L	250	4-Stroke	8M0142979	Pro XS/Verado, S/N 1E080500 & Up
Mercury/Mariner	V8 4.6L	300	4-Stroke	8M0142979	Pro XS/Verado, S/N 2B529482 & Up
Mercury/Mariner	V8 Racing	300R	4-Stroke	8M0142979	S/N 1E080500 & Up
Mercury/Mariner	V8 Racing	AMS Racing	4-Stroke	8M0142979	S/N 1E081459 & Up

Technical Specs

Product Type: Gearcase Seal Kit
Installation: Direct OEM replacement
Dimensions: 14.5" L x 20.6" W x 3.2" H
Weight: 0.57 lbs (0.26 kg)
Other Technical Attributes: Includes necessary seals and O-rings for lower unit service

What’s in the Box

1 x Gearcase Seal Kit (Replaces 8M0142979/26-8M0142979)

Installation Notes

Disconnect the battery and ensure the engine is in a secure, stable position.
Drain the gearcase lubricant by removing the drain and vent plugs.
Remove the propeller and its associated hardware.
Unbolt and carefully lower the gearcase from the driveshaft housing.
Systematically disassemble the necessary components, noting the location of each seal and O-ring being replaced.
Thoroughly clean all parts and sealing surfaces, removing any old sealant or gasket residue.
Carefully install the new seals and O-rings from the kit, lightly lubricating them with marine grease as needed.
Reassemble the gearcase, ensuring all components are correctly seated and torqued to manufacturer specifications.
Reinstall the gearcase assembly and propeller.
Refill the lower unit with the correct type and amount of gear lubricant according to your owner's manual.
Check for any leaks before returning the engine to service.

Troubleshooting & FAQ

How do I know if this seal kit fits my engine?

This kit is specifically for Mercury/Mariner 175-300HP V6/V8 four-stroke models. It's critical to verify your engine's serial number against the ranges listed in the compatibility table (e.g., 2B529482 and up for most models). Do not rely on horsepower or year alone.

What are the signs of a failing gearcase seal?

Common signs include milky, water-contaminated gear lube (visible during a lube change), visible oil leaks around the propeller shaft or lower unit housing, or a persistent low lubricant level that requires frequent top-offs.

Does this kit include everything for a lower unit service?

This kit contains the primary seals and O-rings required for servicing the gearcase itself. However, it does not typically include seals for other components like the water pump, which is often serviced at the same time and requires a separate kit.

My serial number is close to the cutoff point. How can I be sure of fitment?

The serial number break is the most accurate way to determine fitment. If your number is the first in the new range (e.g., exactly 2B529482), this kit is correct. If your number is just before the break, you will likely need the previous part number. When in doubt, consult your engine's official parts manual.

What is the recommended replacement interval?

There is no fixed hour or time interval. It is best practice to replace gearcase seals whenever the lower unit is removed for service or if any leaks are detected. Seals should be visually inspected for leaks during annual service.

Is this an aftermarket or OEM part?

This listing is for an aftermarket replacement part, not an OEM component. It has been manufactured to meet or exceed OEM-level specifications with comparable materials in an ISO 9002 certified facility and is batch-inspected for quality and consistency.

What are the shipping speed and cost?

We ship worldwide quickly, with typical transit times of 5–15 days for most regions. Standard shipping is free for most orders, and any available expedited options with associated costs will be displayed at checkout.

What is the warranty and return policy?

This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. See our full policy page or reach out for instructions.

Safety & Important Info

Verify images and specifications against your original part before purchase. If anything differs—even if your model appears on a compatibility list—do not purchase.
This is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
Professional installation is strongly recommended for safety, proper function, and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
Fast Global Fulfillment — We offer free standard delivery to most regions, with an average transit time of 5–15 days.
Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.

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