Lower Unit Gearcase Seal Kit – Fits Mercury/Mariner 30-125 HP (Replaces 26-43035A4)
Lower Unit Gearcase 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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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 30-125 HP (Repl...
Product Details
This Lower Unit Gearcase Seal Kit is a direct replacement for Mercury and Mariner outboard engines from 30 to 125 HP. It covers both 2-stroke and 4-stroke models manufactured between 1991 and 2010, designed to fit lower units with either a 3-jaw or 6-jaw reverse clutch mechanism.
This kit provides a direct interchange for Mercury part numbers 26-43035A4, 26-43035A3, 26-43035A2, and 26-43035A1, as well as aftermarket equivalents like Sierra 18-2626, GLM 87590, and Mallory 9-74200.
- Engineered for direct replacement with no modifications needed.
- Compatible with both 3-jaw and 6-jaw reverse clutch systems.
- Includes a comprehensive set of seals, gaskets, and o-rings for a complete overhaul.
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 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercury/Mariner owners, this kit fits a wide range of 2-stroke and 4-stroke models from 1991 onwards, including Bigfoot variants. Check your serial number for specific newer models to ensure fitment.
For Force outboards, this kit is compatible with select 75, 90, and 120 HP models from the mid-to-late 1990s.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury/Mariner | 2-Stroke | 100/115/125 | 2-Stroke | 1991+ | 26-43035A4 | USA 0B209468 and newer, Belgium 9523034 and newer, with either 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 | |
| Mercury/Mariner | 4-cyl | 45-90 | 2-Stroke | 1991–2010 | 26-43035A4 | |
| Mercury | Outboard | 30 | 2-Stroke | 1999–2001 | 26-43035A4 | |
| Mercury | Outboard | 40 | 2-Stroke | 1995–2007 | 26-43035A4 | |
| Mercury | Outboard | 45 | 2-Stroke | 1991–2004 | 26-43035A4 | |
| Mercury | Outboard | 50 | 2-Stroke | 1991–2007 | 26-43035A4 | Excluding 2003–2005 |
| Mercury | Outboard | 55 | 2-Stroke | 1991–2006 | 26-43035A4 | |
| Mercury | Outboard | 60 | 2-Stroke | 1991–2007 | 26-43035A4 | |
| Mercury | Outboard | 65 | 2-Stroke | 1994–1998 | 26-43035A4 | |
| Mercury | Outboard | 70 | 2-Stroke | 1983, 1987–1990 | 26-43035A4 | |
| Mercury | Outboard | 75 | 2-Stroke | 1987-up | 26-43035A4 | |
| Mercury | Outboard | 80 | 2-Stroke | 1987–1990, 2005-up | 26-43035A4 | |
| Mercury | Outboard | 90 | 2-Stroke | 1987-up | 26-43035A4 | |
| Mercury | Outboard | 100 | 2-Stroke | 2001–2007 | 26-43035A4 | |
| Mercury | Outboard | 115 | 2-Stroke | 1994–1996, 2001-up | 26-43035A4 | |
| Mercury | Outboard | 125 | 2-Stroke | 1997–2000, 2004-up | 26-43035A4 | |
| Force | Outboard | 75 | 2-Stroke | 1999 | 26-43035A4 | |
| Force | Outboard | 90 | 2-Stroke | 1995–1999 | 26-43035A4 | |
| Force | Outboard | 120 | 2-Stroke | 1995–1999 | 26-43035A4 |
Technical Specs
- Product Type
- Lower Unit/Gearcase Seal Kit
- Installation
- Direct replacement
- Compatibility
- Compatible with lower units featuring either 3-jaw or 6-jaw reverse clutch
- Warranty
- Varies by supplier (typically 1-year)
What’s in the Box
- Various oil seals
- Various gaskets
- Various O-rings
- Drain screw gasket(s)
- Water line seal(s)
- Impeller gasket(s)
- Washer(s)
- Insulator bushing(s)
- Drive shaft oil seal(s)
Installation Notes
- Position the outboard engine securely on a stand or with the lower unit accessible.
- Place a drain pan under the gearcase and remove the gear lube drain and vent screws. Allow all oil to drain completely.
- Remove the bolts securing the lower unit to the engine housing and carefully separate it.
- Following your service manual, disassemble the gearcase to access the old seals, gaskets, and o-rings.
- Carefully remove all old seals and gaskets, ensuring the sealing surfaces are clean and free of debris or corrosion.
- Install the new seals and components from the kit, lightly lubricating them with marine grease or clean gear oil as specified.
- Reassemble the gearcase, torquing all fasteners to the manufacturer's specifications.
- Re-install the lower unit onto the engine.
- Refill the gearcase with the correct type and amount of marine gear lubricant through the lower drain hole until it flows out the upper vent hole.
- Install the vent and drain screws with new gaskets. After a short period, check for any signs of leaks.
Troubleshooting & FAQ
How do I know if this seal kit will fit my specific engine model?
This kit is designed for a broad range of Mercury, Mariner, and Force engines. The best way to confirm fitment is to check your model, HP, and year against the compatibility table on this page. For certain Mercury/Mariner models, you may also need to verify your engine's serial number is within the specified range.
What are the common signs that my gearcase seals are failing?
The most common sign is milky, light-colored gear lube, which indicates water intrusion. You may also notice oil leaking from the propeller shaft area or around the drain/vent screws. In some cases, a grinding noise from the lower unit can signal lubrication failure due to water contamination.
Does this kit fit both 3-jaw and 6-jaw reverse clutches?
Yes, this kit contains the necessary components to service lower units equipped with either the 3-jaw or 6-jaw reverse clutch designs found in the specified engine models.
How often should lower unit seals be replaced?
As a preventative measure, it's good practice to inspect your gear lube annually or every 100 hours. Many mechanics recommend replacing the seals every 3-5 years, or immediately if you notice any signs of water intrusion or oil leaks. It's also wise to replace them whenever the gearcase is disassembled for other service.
What is the difference between this aftermarket kit and an OEM one?
This is an aftermarket part designed to meet or exceed original manufacturer (OEM) specifications for fit, form, and function. It uses comparable materials and is produced in an ISO 9002 certified facility, offering a reliable, cost-effective alternative to OEM parts.
What is your shipping speed and cost?
We ship worldwide quickly—typical transit is 5–15 days for most regions. Standard shipping is free on all orders. Expedited shipping options and associated costs, if available for your location, will be presented at checkout.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. Please see our full policy page or contact us 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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