Upper Unit Seal Kit – Fits MerCruiser Alpha One Gen I (Replaces 26-32511A1)
Upper Unit Seal Kit – Fits MerCruiser Alpha One Gen I (Replaces 26-32511A1) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Upper Unit Seal Kit – Fits MerCruiser Alpha One Gen I (Replaces 26-...
Product Details
This Upper Unit Seal Kit – Fits MerCruiser Alpha One Gen I (Replaces 26-32511A1) provides all necessary components to reseal the upper driveshaft housing on MerCruiser R, MR, and Alpha One Generation I sterndrives from 1978–1990. It is also compatible with #1 units and 888 stern drives with serial numbers 3106717 and up.
This kit is a direct aftermarket replacement for Mercury Marine 26-32511A1 and 26-32511B1, Sierra 18-2648, GLM 87500, Mallory 9-74303, and Red Rhino MR-155.
- Installs in the upper driveshaft housing.
- Comprehensive kit includes all required seals, gaskets, and O-rings for a complete service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury Marine | 26-32511A1 |
| Mercury Marine | 26-32511B1 |
| Sierra | 18-2648 |
| GLM | 87500 |
| Mallory | 9-74303 |
| Red Rhino | MR-155 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is designed for a wide range of MerCruiser sterndrives from 1978 to 1995. Please verify your model and serial number against the list below to ensure a perfect match.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 120/140 | 120/140 | 4-Stroke | 1978–1982 | 26-32511A1 | Serial #4893635-6225576 |
| MerCruiser | 165 | 165 | 4-Stroke | 1978–1981 | 26-32511A1 | Serial #4890460 & Up |
| MerCruiser | 228 | 228 | 4-Stroke | 1978–1982 | 26-32511A1 | Serial #4898730-6225576 |
| MerCruiser | 260 | 260 | 4-Stroke | 1978–1982 | 26-32511A1 | Serial #4898730-6225576 |
| MerCruiser | 470 | 170 | 4-Stroke | 1978–1982 | 26-32511A1 | Serial #4893835-6225576 |
| MerCruiser | 485 | 185 | 4-Stroke | 1980–1982 | 26-32511A1 | Serial #4893835 & Up |
| MerCruiser | 898 | 228 | 4-Stroke | 1978–1982 | 26-32511A1 | Serial #4898730-6225576 |
| MerCruiser | R/MR/Alpha One | Various | 4-Stroke | 1983–1990 | 26-32511A1 | Sterndrive Serial #6225577-0F386995 |
| MerCruiser | R/MR/Alpha One | Various | 4-Stroke | 1983–1990 | 26-32511A1 | Transom Assembly Serial #6216687-0F386995 |
| MerCruiser | Alpha One SS | Various | 4-Stroke | 1986–1989 | 26-32511A1 | ALL Serial Numbers |
| MerCruiser | SSM II/III/IV/V | Various | 4-Stroke | 1982–1995 | 26-32511A1 | ALL Serial Numbers |
Technical Specs
- Product Type
- Upper Unit Seal Kit
- Installation
- Upper Driveshaft Housing
- Weight
- 0.25 lb (113 g)
- Length
- 12.0 in (304.8 mm)
- Width
- 11.0 in (279.4 mm)
- Height
- 3.0 in (76.2 mm)
- GTIN
- 745061074897
What’s in the Box
- 1 x Water Pocket Cover Gasket (18-0894)
- 1 x Oil Seal (18-2003)
- 1 x Oil Seal (18-2049)
- 1 x Oil Seal (18-2056)
- 1 x Seal Ring (18-2944)
- 2 x Drain Screw Gasket (18-2945)
- 1 x Water Pump Housing Bushing (18-3110)
- 2 x O-ring (18-7153)
- 1 x O-ring (18-7161)
- 1 x O-ring (18-7169)
- 1 x O-ring (18-7445)
- 1 x Water Tube Rubber Seal (18-0521)
Installation Notes
- Drain the gear lube from the sterndrive completely.
- Remove the upper unit from the lower unit housing, following the manufacturer's service manual procedures.
- Carefully disassemble the upper driveshaft housing, taking note of the order and orientation of all components.
- Thoroughly clean all mating surfaces and remove any old gasket material or sealant residue.
- Inspect shafts and housing bores for wear or damage before installing new seals.
- Using appropriate seal drivers or a press, install the new oil seals and O-rings from the kit. Ensure they are seated correctly and not damaged during installation.
- Reassemble the unit with the new gaskets.
- Once reassembled, perform a vacuum and pressure test to confirm the integrity of the new seals before reinstalling the sterndrive.
- Refill the sterndrive with the correct type and amount of new gear lube.
Troubleshooting & FAQ
How do I know if this seal kit fits my MerCruiser sterndrive?
The best way to confirm fitment is to check your sterndrive's model, year, and serial number against the compatibility chart provided on this page. This kit fits a specific range of R, MR, Alpha One, and other models.
What are the signs my upper unit seals are failing?
Common symptoms include milky, water-contaminated gear lube, visible oil leaks around the upper housing of the sterndrive, or a failure to hold pressure during a routine service test.
Is this kit for the upper or lower part of the sterndrive?
This is an upper unit seal kit, designed specifically for servicing the upper driveshaft housing and related components.
Do I need special tools to install this kit?
Yes, professional installation is recommended. Specialized tools such as a bearing and seal driver set, a press, and a drive pressure/vacuum tester are typically required for a correct and leak-free installation.
How often should these seals be replaced?
Seals should be inspected for leaks annually. It is good practice to replace them as a preventative measure every few seasons, or any time the sterndrive is disassembled for other service.
What is the difference between this kit and the OEM version?
The seals, gaskets, and O-rings in this kit are engineered from high-quality materials designed to meet or exceed original equipment manufacturer (OEM) specifications for performance and durability in the 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
- 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.
Payment & Security
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