Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen II Stern Drives (Replaces 803099T1, 30-803099T1, 18-8218)

Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen II Stern Drives (Replaces 803099T1)

This complete service kit is for MerCruiser Alpha One Gen II stern drives manufactured from 1991 through current production, specifically for serial numbers 0D469859 and up. It contains all the necessary bellows, gaskets, a gimbal bearing, and hardware required to completely seal the transom opening and maintain the integrity of your stern drive system.

This kit is a direct aftermarket replacement for Mercury/MerCruiser 803099T1 / 30-803099T1, Sierra 18-8218, Sierra 18-8206-1 (which includes a greasable bearing), Mallory 9-72900 / 9-72906, Red Rhino MR-907, GLM 21960, and SEI 9A-116.

• Complete Assembly: Includes U-joint, exhaust, and shift bellows, plus a gimbal bearing, gaskets, and hardware.
• Precise Fitment: Engineered for MerCruiser Alpha One Gen II drives (1991+) with serial numbers 0D469859 and higher.
• Durable Materials: Constructed from high-quality rubber and elastomer compounds to withstand the harsh marine environment.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x U-Joint Bellow w/ Sleeve & Clamp (Replaces 816431A1)
• 1 x Exhaust Bellow w/ Clamp (Replaces 18654A1 / 8M0124227)
• 1 x Shift Cable Bellow w/ Clamp (Replaces 74639A2)
• 1 x Gasket Kit (Replaces 94996Q2)
• 1 x Gimbal Bearing (Replaces 879194A02)
• 4 x Grounding Clips
• 1 x Water Hose 3/4" (Replaces 8M0215001)
• 5 x Zip Ties
• 1 x Bell Housing Gasket Set

Installation Guide

Performing a transom seal repair is a significant task that requires specialized tools and mechanical expertise. We highly recommend professional installation.

1. Safety First: Disconnect the boat's battery.
2. Remove Stern Drive: Carefully detach the Alpha One Gen II stern drive from the bell housing.
3. Remove Old Components: Detach and discard the old u-joint, exhaust, and shift bellows, along with their clamps.
4. Extract Bearing: Remove the old gimbal bearing from the transom assembly using a slide hammer or bearing puller tool.
5. Clean Surfaces: Thoroughly clean all mating surfaces on the gimbal housing and bell housing, removing any old sealant or gasket residue.
6. Install New Bearing: Press the new gimbal bearing into place using a proper bearing driver and alignment tool to ensure it is seated correctly.
7. Install Bellows: Install the new u-joint, exhaust, and shift bellows. Use bellows adhesive and secure all clamps tightly.
8. Final Assembly: Install the new gasket set and reinstall the stern drive. Ensure all connections are secure.
9. Test: Once assembled, check for proper shift operation and run the engine to check for any water leaks around the transom.

Troubleshooting & FAQ

How do I confirm this fits my Alpha One Gen II drive?
This kit is specifically designed for MerCruiser Alpha One Gen II stern drives manufactured from 1991 to the present. The most important factor is the serial number, which must be 0D469859 or higher. Please locate and verify your drive's serial number before ordering to guarantee fitment.

What are the signs that my transom bellows need replacing?
Common signs of a failing transom seal include water collecting in the bilge area, a roaring or grinding noise from the gimbal bearing (indicating water intrusion and failure), or visible cracks, stiffness, or holes in the rubber bellows. Regular visual inspection is crucial for preventative maintenance.

This kit has a sealed bearing. What's the difference compared to a greasable one?
Our kit includes a high-quality sealed gimbal bearing, which is designed to be maintenance-free, just like the original OEM part. Some aftermarket alternatives offer a "greasable" bearing (like Sierra 18-8206-1) which requires periodic greasing but may offer a longer life if properly maintained. This sealed bearing provides install-and-forget reliability.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.