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

MerCruiser Alpha One Gen II Transom Seal Kit – Fits MerCruiser Alpha One Gen II Drives (Replaces 30-803099T1)

This complete transom seal kit is designed for MerCruiser Alpha One Gen II stern drives from 1991 to the present (serial numbers 0D469859 & up). The kit includes all necessary bellows, a greasable gimbal bearing, and hardware for a full service.

This is a direct replacement for Sierra part number 18-8206-1 and Mercury/Quicksilver part numbers 30-803099T1 and 803099T1.

• Includes U-Joint, Exhaust, and Shift Cable bellows.
• Comes with a greasable gimbal bearing for easier maintenance.
• Engineered for a direct-fit installation.

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.

Note: 1998 and newer models may require the purchase of Sierra 18-21005 Gimbal bearing if not included in your specific kit. This kit includes the greasable version of this bearing.

Technical Specifications

Package Contents

• 1 x U-Joint Bellows
• 1 x Exhaust Bellows
• 1 x Shift Cable Bellows
• 1 x Gimbal Bearing (Greasable 18-21005)
• 1 x 3/4"-ID Water Hose
• 1 x Mounting Gasket

Installation Guide

1. Safety First: Disconnect the boat's battery before beginning any work.
2. Remove the Outdrive: Detach the MerCruiser Alpha One Gen II outdrive from the transom assembly according to your service manual.
3. Remove Old Bellows: Carefully cut and remove the old U-joint, exhaust, and shift cable bellows. Remove the stainless steel clamps.
4. Extract Gimbal Bearing: Use a slide hammer with a bearing puller attachment to remove the old gimbal bearing from the transom housing.
5. Clean Surfaces: Thoroughly clean the transom housing and all mounting surfaces, removing any old sealant or debris.
6. Install New Bearing: Drive the new gimbal bearing into place, ensuring the grease hole is correctly aligned for future maintenance.
7. Install New Bellows: Install the new shift cable, U-joint, and exhaust bellows. Use the provided clamps and ensure they are securely fastened to prevent leaks.
8. Reassemble: Re-install the outdrive onto the transom assembly using the new mounting gasket and o-rings included in the kit.
9. Final Checks: Reconnect the battery. Once in the water, check for any leaks around the transom assembly.

Troubleshooting & FAQ

How do I confirm this fits my engine?
This kit is specifically for MerCruiser Alpha One Gen II stern drives manufactured from 1991 to present. It is crucial that your drive's serial number is 0D469859 or newer. Please verify your model and serial number before purchasing.

What are the signs my transom seals are failing?
Common symptoms include water in your bilge, a groaning or grinding noise from the gimbal bearing when turning the outdrive, or visible cracks and brittleness on the rubber bellows.

Does this kit include a greasable gimbal bearing?
Yes, this kit comes with a greasable gimbal bearing (Sierra 18-21005), which allows you to lubricate the bearing easily for extended service life.

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.