Lower Unit Seal Kit – Fits Mercury/Mariner 30-125 HP (Replaces 26-43035A4)

$67.15 $107.00

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Lower Unit Seal Kit – Fits Mercury/Mariner 30-125 HP (Replaces 26-43035A4) is backordered and will ship as soon as it is back in stock.

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Product Details

This Lower Unit Seal Kit – Fits Mercury/Mariner Outboard 30-125 HP (Replaces 26-43035A4) is designed for various 2-stroke and 4-stroke models from approximately 1991 to 2010. It is compatible with outboards using either a 3-jaw or 6-jaw reverse clutch, providing a reliable solution for gearcase maintenance and repair.

It serves as a direct replacement for OEM part numbers 26-43035A4, 26-43035A3, 26-43035A2, and 26-43035A1. It is also a direct cross-reference for Sierra 18-2626, GLM 87590, and Mallory 9-74200.

Engineered for direct replacement of the original lower unit seals.
Compatible with applications using either a 3-jaw or 6-jaw reverse clutch.
Includes all necessary seals and gaskets for a comprehensive lower unit service.

Part Number Matrix

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

Brand	Part Number	Notes
Mercury	26-43035A4	Supersedes 26-43035A3, 26-43035A2, 26-43035A1
Sierra	18-2626	Aftermarket interchange
GLM	87590	Aftermarket interchange
Mallory	9-74200	Aftermarket interchange

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit is designed for a wide range of Mercury and Mariner 2-stroke and 4-stroke outboards. Pay close attention to serial numbers and BIGFOOT model designations.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury/Mariner	2-Stroke	100/115/125	2-Stroke	1991+	26-43035A4	USA 0B209468+, BEL 9523034+; with 3 or 6 jaw reverse clutch
Mercury/Mariner	4-Stroke BIGFOOT	50	4-Stroke	1991–2010	26-43035A4
Mercury/Mariner	3-cyl BIGFOOT	60	4-Stroke	1991–2010	26-43035A4
Mercury/Mariner	3-cyl	70	4-Stroke	1991–2010	26-43035A4	USA 0A996142+ / BEL 9483121+
Mercury/Mariner	3-cyl	75	4-Stroke	1991–2010	26-43035A4	USA 0C222000+ / BEL 9589039+
Mercury/Mariner	3-cyl	80/90	4-Stroke	1991–2010	26-43035A4
Mercury/Mariner	4-cyl	100/115/125	4-Stroke	1991–2010	26-43035A4
Mercury/Mariner	3-cyl	30-90	2-Stroke	1991–2010	26-43035A4	As reported by EMP
Mercury/Mariner	4-cyl	45-90	2-Stroke	1991–2010	26-43035A4	As reported by EMP

Compatibility with Force outboards from 1991–1999 is also reported by various aftermarket sources.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Force	Outboard	30-125	2-Stroke	1991–1999	26-43035A4	Compatibility reported by various retailers

Technical Specs

Product Type: Lower Unit/Gearcase Seal Kit
Installation: Direct replacement
Technical Note: For applications with either 3-jaw or 6-jaw reverse clutch

What’s in the Box

Seals and gaskets for lower unit/gearcase (replaces 26-43035A4)

Installation Notes

Disconnect the battery and shift the outboard into a neutral gear.
Place a drain pan under the lower unit and remove both the upper vent and lower drain screws to empty the gearcase oil.
Remove the propeller assembly.
Unbolt and carefully detach the lower unit from the engine's upper housing.
Disassemble the gearcase as needed to access and replace all old seals, gaskets, and O-rings with the new ones from the kit. Ensure all mating surfaces are clean and free of old gasket material.
Reassemble the lower unit components, ensuring proper alignment and seating of all parts.
Re-install the lower unit to the engine housing, torquing bolts to manufacturer specifications.
With the lower unit vertical, fill the gearcase with the recommended marine gear lube through the bottom drain hole until it flows out the top vent hole.
Install the vent screw first, then the drain screw. Clean any excess oil and check for leaks after a short period.

Troubleshooting & FAQ

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

Always check your engine's serial number against the ranges provided in the compatibility table. This kit fits Mercury/Mariner 2-stroke models with USA serial number 0B209468 and newer or Belgium serial number 9523034 and newer, as well as specific 4-stroke models with listed serial numbers.

What are the signs that my lower unit seals are failing?

Common indicators include milky or cloudy gear oil (indicating water intrusion), visible oil leaks around the propeller shaft or driveshaft, or metal shavings in the drained oil. Any of these signs warrant an inspection and seal replacement.

What is the difference between a 3-jaw and 6-jaw reverse clutch?

The jaw count refers to the design of the reverse gear clutching mechanism inside the gearcase. This kit is designed to be compatible with lower units that have either the 3-jaw or 6-jaw configuration within the specified engine models.

How often should I replace the lower unit seals?

There is no fixed interval, but seals should be inspected during every annual service or whenever the gear oil is changed. It is good practice to replace them every few years as preventative maintenance, or immediately if any signs of leakage are found.

Are special tools required for this installation?

While basic hand tools are sufficient for much of the job, specialized tools like a bearing puller, seal driver, or pressure/vacuum tester may be necessary for proper installation and to ensure a leak-free result. A service manual for your specific engine is highly recommended.

What kind of gear lube should I use after installation?

Use a high-quality marine gear lube that meets your engine manufacturer's specifications (e.g., API GL-5 rated). Do not use standard automotive gear oil, as it lacks the necessary emulsifiers and corrosion inhibitors for a marine environment.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

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