Transom Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 30-803099T1, 803099T1)
Transom Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 30-803099T1, 803099T1) 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 30-80...
Product Details
This MerCruiser Alpha One Gen II Transom Seal Kit is designed for MerCruiser Alpha One Gen II stern drives manufactured from 1991 to the present (serial numbers 0D469859 and up). The kit provides all components required for a comprehensive transom service, ensuring a precise fit and reliable performance.
It serves as a direct interchange for Sierra part number 18-8206-1 and is cross-referenced with Mercury/Quicksilver equivalents 30-803099T1 and 803099T1.
- Engineered for direct replacement, simplifying installation.
- Includes all essential bellows, gaskets, and a greasable gimbal bearing.
- Constructed with durable rubber/neoprene bellows and marine-grade stainless steel clamps.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-8206-1 |
| Quicksilver/Mercury | 30-803099T1 |
| Mercury | 803099T1 |
Engine & Model Compatibility
Confirm your engine model and year in the table below. This kit is specifically designed for the following MerCruiser models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen II | All | 4-Stroke | 1991–Present | 30-803099T1 | For serial numbers 0D469859 & up |
Technical Specs
- Product Type
- Transom Seal Kit
- Installation
- Direct replacement
- Housing Material
- Rubber/Neoprene bellows, marine-grade stainless steel clamps
- Housing Color
- Black
- Dimensions
- Kit size approx. 25 × 22 × 20 cm (9.8 × 8.7 × 7.8 inches)
- Weight
- 2 kg (4.4 lbs)
- Fitting Type
- Direct fit for Alpha One Gen II
- Warranty
- Limited lifetime (Sierra)
- Other Technical Attributes
- Includes greasable gimbal bearing
What’s in the Box
- 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 Notes
- Begin by disconnecting the battery and ensure the vessel is safely and securely positioned.
- Remove the sterndrive unit from the transom assembly according to the manufacturer's service manual.
- Carefully detach and remove the old U-joint, exhaust, and shift bellows, along with the gimbal bearing.
- Thoroughly clean all mating surfaces on the transom and bell housing, removing any old gasket material or corrosion.
- Press the new gimbal bearing into place using a proper bearing driver tool, ensuring it is correctly seated.
- Install the new shift cable, exhaust, and U-joint bellows, confirming they are correctly aligned and sealed.
- Secure all bellows with their respective stainless steel hose clamps, tightening them to the specified torque.
- Fit the new water intake hose and install the new mounting gaskets and O-rings included in the kit.
- Reinstall the sterndrive, verifying proper engine alignment and shift mechanism engagement.
- After reassembly, reconnect the battery and conduct a leak test in the water before full operation.
Troubleshooting & FAQ
Will this kit fit my 1999 Alpha One Gen II drive?
Yes, this kit is designed for all MerCruiser Alpha One Gen II drives from 1991 to present. The included greasable gimbal bearing (18-21005) is the correct type for your drive. The note regarding 1998 and newer models is to ensure the correct bearing is used, which this kit provides.
What are the signs that my transom seals are failing?
Common signs of failing transom seals include water entering the bilge area, a roaring or grinding noise from the gimbal bearing when turning the helm, or visible cracks, holes, or deterioration on the rubber bellows.
How often should these bellows be replaced?
For preventative maintenance, it is recommended to inspect transom bellows annually for any signs of wear, such as cracking or dry rot. A full replacement is typically advised every 3-5 years, depending on usage and environmental conditions (saltwater vs. freshwater).
How does the included gimbal bearing differ from an OEM one?
This kit features a greasable gimbal bearing. Unlike many sealed OEM bearings, this design allows for periodic lubrication via a grease fitting, which can help extend its operational life by purging contaminants and maintaining smooth rotation.
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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