Transom Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 803099T1, 18-8206-1)
Transom Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 803099T1, 18-8206-1) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Transom Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 80309...
Product Details
This complete Transom Seal Kit – Fits MerCruiser Alpha One Gen II is engineered for all MerCruiser Alpha One Generation 2 stern drives manufactured from 1991 to the present. The kit includes all the critical bellows, a greasable gimbal bearing, gaskets, and a water hose needed to fully service the transom assembly and maintain watertight integrity.
This kit serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury/Quicksilver 803099T1 / 30-803099T-1, Sierra 18-8206-1, Mallory 9-72904, and Red Rhino MR-907.
- Installation requires mechanical expertise for a direct fit.
- Made from durable rubber/neoprene with stainless steel hardware.
- Includes essential components for a complete transom seal repair.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury / Quicksilver | 803099T1 |
| Mercury / Quicksilver | 30-803099T-1 |
| Sierra | 18-8206-1 |
| Mallory | 9-72904 |
| Red Rhino | MR-907 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen II | All | 4-Stroke | 1991–Present | 803099T1 | Fits serial numbers 0D469859 & Up |
Technical Specs
- Product Type
- Transom Seal Kit
- Installation
- Direct replacement, requires mechanical expertise
- Housing Material
- Rubber/Neoprene bellows with stainless steel clamps
- Housing Color
- Black
- Weight
- 2.00 kg (4.4 lb)
- Fitting Type
- Direct fit to Alpha One Gen II
- Warranty
- Varies by brand - typically 1 year limited warranty
- Other Technical Attributes
- Complete kit for transom seal repair
What’s in the Box
- 1 x Universal Joint Bellows Assembly (816431A1)
- 1 x Exhaust Bellow (8M0124227)
- 1 x Shift Actuating Cable Bellows Assembly (74639A2)
- 1 x Gimbal Bearing (879194A02)
- 1 x 3/4 Inch Inside Diameter Hose (8M0215001)
- 1 x Bell Housing Gasket Set (94996Q2)
Installation Notes
- Disconnect the battery and trim the sterndrive to the trailer position.
- Remove the sterndrive unit according to manufacturer guidelines to access the transom assembly.
- Carefully remove the old U-joint, exhaust, and shift cable bellows. Note the orientation of clamps.
- Extract the old gimbal bearing using a slide hammer or bearing puller tool.
- Thoroughly clean all mounting surfaces on the transom and bell housing, removing any old sealant or debris.
- Install the new gimbal bearing, ensuring it is properly seated and greased.
- Install the new bellows, starting with the shift cable, then exhaust, and finally the U-joint bellow.
- Secure all bellows with the provided clamps and verify they are sealed.
- Install the new gaskets and re-mount the sterndrive unit.
- Once assembled, lower the drive and check for water leaks in a controlled environment before open water use.
Troubleshooting & FAQ
Will this kit fit my MerCruiser Alpha One Gen I drive?
No. This kit is specifically designed for Alpha One Gen II sterndrives (1991 and newer). Gen I drives require a different seal kit.
What are the signs my transom seals are failing?
Common symptoms include water inside the U-joint bellows, a roaring or grinding noise from a worn gimbal bearing, or difficulty shifting, which may indicate a damaged shift cable bellow. Regular inspection is key.
How often should these seals be replaced?
As a preventative measure, it is recommended to inspect bellows annually and replace the entire kit every 5-7 years, or sooner if you observe any cracks, dry rot, or water intrusion.
Does this kit include everything I need?
This kit includes all standard seals, bellows, gaskets, and the gimbal bearing for a typical transom service. However, it does not include specialized tools like a bellow expander, hinge pin tool, or alignment tool, which are required for installation.
Is the included gimbal bearing greasable?
Yes, this kit includes a high-quality greasable gimbal bearing (Part: 879194A02) to ensure smooth, long-lasting operation.
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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