Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner/Force 30-125 HP (Replaces 26-43035A4, 18-2626)
Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner/Force 30-125 HP (Replaces 26-43035A4, 18-2626) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner/Force 30-125 HP...
Product Details
This Lower Unit Gearcase Seal Kit is designed for a wide range of Mercury, Mariner, and Force outboards. It provides the essential seals and gaskets for servicing the lower unit on 30–125 HP 2-stroke and 4-stroke models from 1983 to current, including Bigfoot, SeaPro, and Marathon models. It also covers Force 75–120 HP outboards from 1995–1999.
The kit serves as a direct replacement for multiple part numbers, including Mercury 26-43035A4, Sierra 18-2626, GLM 87590, and Mallory 9-74200, ensuring broad interchange compatibility for a complete gearcase rebuild.
- Engineered for direct replacement with no modifications needed.
- Designed specifically for models with a 4.25" (107.95mm) gearcase diameter.
- Kit contains all necessary gaskets and seals for a standard lower unit service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 26-43035A4 |
| Mercury | 26-43035A3 |
| Mercury | 26-43035A2 |
| Mercury | 26-43035A1 |
| Sierra | 18-2626 |
| GLM | 87590 |
| Mallory | 9-74200 |
| YiheoZux | 26-43035A4 |
| SeaSierra | 26-43035A4 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit fits various 2-stroke and 4-stroke Mercury/Mariner outboards from 30 HP to 125 HP, including Optimax and Pro XS models with a 4.25" gearcase.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 3 & 4-CYL Bigfoot | 30-125 | 2- & 4-Stroke | 1987-current | 26-43035A4 | 4.25" (107.95mm) gearcase |
| Mercury | 4-Stroke | 30 | 4-Stroke | 1999–2001 | 26-43035A4 | 3-cylinder models |
| Mercury | 4-Stroke | 40 | 4-Stroke | 1995–2007 | 26-43035A4 | |
| Mercury | 4-Stroke | 45 | 4-Stroke | 1991–2004 | 26-43035A4 | |
| Mercury | 4-Stroke | 50 | 4-Stroke | 1991–2002, 2006–2007 | 26-43035A4 | Includes Bigfoot models |
| Mercury | 4-Stroke Bigfoot | 50 | 4-Stroke | 1995–2000 | 26-43035A4 | |
| Mercury | 4-Stroke | 55 | 4-Stroke | 1991–2006 | 26-43035A4 | |
| Mercury | 4-Stroke | 60 | 4-Stroke | 1991–2007 | 26-43035A4 | Includes 3-cyl Bigfoot models |
| Mercury | 3-cyl Bigfoot | 60 | 2-Stroke | 1997–2004 | 26-43035A4 | SeaPro/Marathon models |
| Mercury | 2-Stroke | 65 | 2-Stroke | 1994–2005 | 26-43035A4 | 3-cylinder models |
| Mercury | 2-Stroke | 70 | 2-Stroke | 1983, 1987–1990 | 26-43035A4 | USA0A996142+ / BEL9483121+ |
| Mercury | 2-Stroke | 75 | 2-Stroke | 1987-up | 26-43035A4 | USA0C222000+ / BEL9589039+ |
| Mercury | 4-Stroke | 75 | 4-Stroke | 2000–2008 | 26-43035A4 | |
| Mercury | 2-Stroke | 80 | 2-Stroke | 1987–1990, 2005-up | 26-43035A4 | |
| Mercury | 4-Stroke | 80 | 4-Stroke | 2006–2010 | 26-43035A4 | |
| Mercury | 2-Stroke | 90 | 2-Stroke | 1987-up | 26-43035A4 | |
| Mercury | 4-Stroke | 90 | 4-Stroke | 2000–2008 | 26-43035A4 | |
| Mercury | 4-Stroke | 100 | 4-Stroke | 2001–2007 | 26-43035A4 | |
| Mercury | 2-Stroke | 115 | 2-Stroke | 1994–1996, 2001-up | 26-43035A4 | With 3 or 6 jaw reverse clutch |
| Mercury | 4-Stroke | 115 | 4-Stroke | 2001–2010 | 26-43035A4 | |
| Mercury | Optimax | 75-125 | 2-Stroke | 2004–2014 | 26-43035A4 | 3-cyl 1.5L models |
| Mercury | Pro XS | 115 | 2-Stroke | 2010–2015 | 26-43035A4 | 3-cyl models |
| Mercury | 2-Stroke | 125 | 2-Stroke | 1997–2000, 2004-up | 26-43035A4 |
For Force outboards, this kit is compatible with select 75, 90, and 120 HP models from the late 1990s.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Force | 3-cyl | 75 | 2-Stroke | 1999 | 26-43035A4 | 3.375 Bore Top Guided |
| Force | 3-cyl | 90 | 2-Stroke | 1995–1999 | 26-43035A4 | 3.375 Bore (Top Guided 1996-1999) |
| Force | 4-cyl | 120 | 2-Stroke | 1995–1999 | 26-43035A4 | 3.375 Bore (Top Guided 1996-1999) |
Technical Specs
- Product Type
- Lower Unit Gearcase Seal Kit
- Installation
- Direct replacement
- Fuel Type
- Gasoline, Diesel
- Housing Color
- Black
- Weight
- 0.08 kg (2.89 oz)
- Warranty
- 1 Year (YiheoZux brand)
- Gearcase Diameter
- For 4.25" (107.95mm) gearcase diameter
What’s in the Box
- 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
Installation Notes
- Disconnect the battery and safely drain the gearcase oil into an approved container.
- Remove the lower unit assembly from the outboard engine. Keep track of all mounting hardware.
- Carefully disassemble the gearcase, noting the position and orientation of shafts, gears, and bearings.
- Remove all old seals, gaskets, and o-rings from the housing and components.
- Thoroughly clean all mating surfaces to ensure they are free of old sealant, corrosion, and debris.
- Install the new seals and gaskets from the kit. Lightly lubricate seals with marine grease before installation.
- Reassemble the gearcase components according to the manufacturer's specifications.
- Reinstall the lower unit onto the outboard, torquing bolts to the proper specification.
- Refill the gearcase with the correct type and amount of new lower unit lubricant.
- After a short run time, re-check the oil for any signs of water intrusion (milky appearance).
Troubleshooting & FAQ
How do I know if this seal kit will fit my specific engine?
This kit fits most Mercury/Mariner 30-125 HP outboards (1983–current) and Force 75–120 HP models (1995–1999) with a 4.25-inch diameter gearcase. To be certain, please cross-reference your engine's model and year against the detailed compatibility tables on this page.
What are the signs that my gearcase seals are failing?
The most common symptoms of a bad gearcase seal are milky, water-contaminated gear oil, visible oil leaks around the propeller shaft or driveshaft, or a distinct burning smell from the lower unit after operation.
How often should I replace my lower unit seals?
It is recommended to inspect your gearcase seals annually. Proactive replacement is advised every 2-3 years as part of regular maintenance, or any time the lower unit is serviced, especially for boats used in saltwater.
Does this kit contain everything to rebuild the gearcase?
This kit contains all the standard, essential seals, gaskets, and o-rings required for a typical lower unit service. It does not include bearings, gears, or other internal hard parts.
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
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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