Lower Gearcase Seal Kit – Fits Mercury/Mercruiser 200/225/250/275/300HP 3.0L V6 (Replaces 26-816575A5)
Lower Gearcase Seal Kit – Fits Mercury/Mercruiser 200/225/250/275/300HP 3.0L V6 (Replaces 26-816575A5) 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 Gearcase Seal Kit – Fits Mercury/Mercruiser 200/225/250/275/3...
Product Details
This Lower Gearcase Seal Kit provides a comprehensive solution for servicing the lower unit on Mercury/Mercruiser 200-300HP, 3.0L V6 engines manufactured between 1994 and 2005. It is designed to fit a wide range of models, including carbureted, EFI/DFI, and high-performance Pro Max and XS variants, ensuring a precise seal to prevent water intrusion and oil leaks.
This kit serves as a direct replacement for Mercury part numbers 26-816575A5 and 816575A5, and interchanges with Sierra 18-2642, GLM 87513, and Mallory 9-74209.
- Engineered for direct-replacement installation.
- Compatible with standard gasoline marine engines.
- Also fits Torquemaster gearcase assemblies.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 26-816575A5 |
| Mercury | 816575A5 |
| Sierra | 18-2642 |
| GLM | 87513 |
| Mallory | 9-74209 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
These seals are designed for specific Mercury and Mercruiser V6 outboards. Please verify your engine's model and serial number against the ranges provided.
| Brand | Model | Rated HP | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Mercury | 200 (DFI Optimax) | 200 | 1997 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G386496–0G589999 |
| Mercury | 225 (3.0L Carb) | 225 | 1994–1998 | 26-816575A5 | 6 Cyl 3.0L, S/N 0D280813–0G760299 |
| Mercury | 225 (3.0L EFI) | 225 | 1995–1998 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G129222–0G760299 |
| Mercury | 225 MARATHON (3.0L Carb) | 225 | 1995–1998 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G245605–0G760299 |
| Mercury | 225 SEAPRO (3.0L Carb) | 225 | 1995–1998 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G245605–0G760299 |
| Mercury | 225 Carb Pro | 225 | 1995–1998 | 26-816575A5 | 6 Cyl 3.0L |
| Mercury | 250 (3.0L EFI) | 250 | 1995–1998 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G129222–0G760299 |
| Mercury | 300 (3.0L EFI) ProMax | 300 | 1998–2005 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G610221–0T105297 |
| Mercury | 300 (3.0L EFI) SuperMagnum | 300 | 26-816575A5 | 6 Cyl 3.0L, S/N 0G610221–0T105297 | |
| Mercury | 300X (3.0L EFI) PRO MAX | 300 | 26-816575A5 | 6 Cyl 3.0L, S/N 0T235084–0T429939 | |
| Mercury | 300X (3.0L EFI) PRO MAX | 300 | 26-816575A5 | 6 Cyl 3.0L, S/N 0T429940–0T999587 | |
| Mercury | 225-300XS DFI EFI | 225-300 | 26-816575A5 | 3.0L V6 |
Technical Specs
- Product Type
- Lower Gearcase Seal Kit
- Installation
- Direct replacement
- Fuel Type
- Compatible with gasoline engines
- Connection
- N/A - internal seals
- Dimensions
- 18.0 in (L) × 12.5 in (W) × 1.5 in (H)
- Weight
- 0.05 kg (0.18 lb)
- Fitting Type
- Lower gearcase internal seals
- Thread Size
- N/A
- Other Technical Attributes
- Fits Torquemaster gearcase assembly
What’s in the Box
- 1 x Lower Gearbox Seal Repair Kit (26-816575A5)
Installation Notes
- Before starting, ensure you have the correct gear lube and new drain screw washers. Disconnect the engine's battery.
- Position a drain pan under the lower unit and remove the upper and lower gear lube drain screws to empty the oil.
- Unbolt and carefully detach the entire lower gearcase assembly from the outboard's midsection.
- Following your engine's service manual, disassemble the gearcase to access the propeller shaft and driveshaft seals.
- Carefully remove all old seals and o-rings, taking care not to scratch the housing surfaces.
- Thoroughly clean all sealing surfaces and component bores of any old sealant or corrosion.
- Install the new seals from the kit using appropriate seal drivers, ensuring they are seated correctly and squarely.
- Reassemble all components in reverse order, torquing fasteners to the manufacturer's specifications.
- Reinstall the lower unit, refill with fresh gear lube from the bottom up until it flows from the top vent hole, then replace both drain screws with new washers.
Troubleshooting & FAQ
Which specific Mercury engines does this seal kit fit?
This kit is designed for a range of Mercury/Mercruiser 200–300HP, 3.0L V6 engines from approximately 1994 to 2005. It covers carbureted, EFI, DFI, Pro Max, and XS models. Always check your engine's serial number against the compatibility table to ensure a perfect match.
What are the signs that my gearcase seals are failing?
Common symptoms of a failed gearcase seal include visible oil leaks around the propeller shaft or lower unit, or milky, water-contaminated gear lube when you drain it. A pressure and vacuum test of the lower unit is the definitive way to diagnose a leak.
Is this kit compatible with both 2-stroke and 4-stroke engines?
The compatibility data primarily points to 3.0L V6 engine blocks, which in this horsepower range and era are typically 2-stroke outboards (e.g., Optimax, Pro Max, EFI). Please verify compatibility based on your specific engine model and serial number, not just the stroke type.
Does this kit include every seal for a complete lower unit overhaul?
This kit contains the primary seals for the lower gearcase housing, driveshaft, and propeller shaft. However, a full overhaul may require other specific gaskets or o-rings not included here. This kit contains all the items shown in the product images.
My engine model is listed, but the year is slightly different. Will it fit?
It's possible, but not guaranteed. Manufacturers often use the same parts across several years, but there can be mid-year changes. The safest method is to verify fitment using your engine's serial number, which is more accurate than the model year alone.
How often should I replace my lower unit seals?
There is no fixed replacement interval. Seals should be replaced whenever the lower unit is disassembled for service (e.g., water pump replacement), if a leak is detected during a pressure test, or if the gear lube shows signs of water contamination.
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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