SeaSierra Mercruiser Alpha One Gen II Upper Unit Seal Kit 88397A1 — Complete O‑rings & Oil Seals for 1991–1996+

The SeaSierra 88397A1 Upper Unit Seal Kit is a complete replacement seal set engineered to restore watertight performance and prevent oil leaks in Mercruiser Alpha One Gen II stern drives.

This SeaSierra kit collects all upper-unit gaskets, O-rings, and oil seals needed when servicing Mercruiser Alpha One (Alpha I) Gen II units. It matches common OEM numbers and fits the model years and serial ranges listed for Alpha One Gen II drives, so you can replace worn seals in one service interval without mixing mismatched parts. The kit is intended for routine maintenance or repair after evidence of oil seepage or water ingress around the upper drive housing.

How do I know this kit fits my Alpha One Gen II drive?

Check the drive serial range and model year: this kit covers Alpha I Gen II units produced in the early 1990s through later serial blocks referenced by manufacturers. Compare the OEM reference numbers stamped on your components to verify compatibility. If your drive matches the listed ranges and part numbers, this kit provides the correct seals for the upper unit service.

• Compatible with Mercruiser Alpha I Gen II 1991–1995 (0D469859 – 0F679999)
• Also fits 1996 & up serials (0F680000 & up)
• Replaces OEM 26-88397A1, 88397A1 and equivalent aftermarket references

What exactly is included in the SeaSierra 88397A1 seal kit?

The kit bundles multiple O-rings, oil seals and gaskets required for a full upper-unit reseal job so you won’t need to source individual parts. Each component is chosen to match form and function of the original seals and to simplify rebuilds. This reduces downtime and the risk of installing mixed-quality or incorrect seals.

• O-rings: 25-25439, 25-35027, 25-35984, 25-70937, 25-32546
• Oil seals: 26-32080, 26-37259 and upper seal 26-88397
• Gaskets and drain hardware: 12-19183/12-20260 drain screw gasket, 26-45577 seal ring gasket

How does installing this kit improve stern drive performance?

Replacing degraded seals restores proper oil retention and keeps water out of the gearcase, which helps prevent bearing damage and gear wear from contamination. Fresh seals also reduce the frequency of leaks and the need to top off gear oil between services. Proper installation returns the unit to intended tolerances and supports longer component life.

• Stops oil leaks at the upper housing and prop shaft area
• Prevents water contamination in the gearcase and bearings
• Supports reliable lubrication and reduces unexpected repairs

What should I prepare before starting the seal replacement?

Gather the correct tools and a service manual for your Alpha One Gen II drive to ensure torque specs and disassembly order are followed. Clean work area and proper supports for the outdrive make the job safer and easier. Inspect adjacent components—shafts, bearings, and housing—for wear to decide if additional parts are needed.

• Service manual or exploded diagram for your exact serial range
• Basic mechanic tools, seal drivers, torque wrench, and cleaner
• Fresh gear oil and a clean container for refilling after assembly

Who this is for: the SeaSierra 88397A1 kit is targeted at marine mechanics, boat owners who perform their own maintenance, and service shops dealing with Mercruiser Alpha One Gen II stern drives. If you maintain or rebuild older Alpha I Gen II units and want a single-source set of correctly matched upper-unit seals, this kit reduces parts searching and helps ensure a consistent reseal job.