Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 Sterndrive (Replaces 30-803099T1)
Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 Sterndrive (Replaces 30-803099T1) 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).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 Sterndriv...
Product Details
This complete Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 Sterndrive (Replaces 30-803099T1) is designed for MerCruiser Alpha One Generation 2 sterndrives manufactured from 1991 and up, with serial numbers 0D469859 and higher. It contains all the essential components to fully service the transom seal assembly, including bellows, gaskets, and a gimbal bearing.
It serves as a direct interchange for Mercury/Quicksilver 30-803099T1/803099T1, Sierra 18-8206-1, GLM 21960, and Mallory 9-72904.
- Engineered for direct OEM replacement and fitment.
- Includes a greasable gimbal bearing for easier maintenance.
- Components are manufactured in an ISO9002 certified facility for quality assurance.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/Quicksilver | 30-803099T1 |
| Mercury/Quicksilver | 803099T1 |
| Sierra | 18-8206-1 |
| GLM | 21960 |
| Mallory | 9-72904 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser sterndrives, this kit is specifically designed for Alpha One Gen 2 models manufactured from 1991 onward with serial number 0D469859 and up.
| Brand | Model | Application | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen 2 | Sterndrive with Exhaust Bellows | 1991–Present | 30-803099T1 | Fits serial number 0D469859 and up |
| MerCruiser | Alpha One Gen 2 | Sterndrive with Exhaust Bellows | 1991–1995 | 30-803099T1 | Serial range 0D469859-0F679999 |
| MerCruiser | Alpha One Gen 2 | Sterndrive with Exhaust Bellows | 1996–1997 | 30-803099T1 | Serial range 0F680000-0K999999 |
| MerCruiser | Alpha One Gen 2 | Sterndrive with Exhaust Bellows | 1998 and up | 30-803099T1 | For greasable gimbal bearing models |
Technical Specs
- Product Type
- Transom Seal Repair Kit
- Installation
- Direct OEM Replacement
- Application
- Alpha One Gen 2 Sterndrive
- Components
- Drive Shaft Bellows, Exhaust Bellows, Shift Cable Bellows, Gaskets
- Includes Gimbal Bearing
- Yes (Greasable Type)
- Housing Material
- High-grade Rubber (Bellows)
- Warranty
- 1 year (OEM Mercury/Quicksilver parts)
- Production Standard
- ISO9002 certified manufacturing (JLM Marine)
- OEM Part Number
- 30-803099T1
- Manufacturer
- Mercury Marine
What’s in the Box
- 1 x Drive Shaft Bellows (816431A1)
- 1 x Exhaust Bellows Assembly (18654A1)
- 1 x Shift Cable Bellows Assembly (74639A2)
- 1 x Water Hose 3/4" (32-41725)
- 1 x Gimbal Bearing (30-60792A4)
- 1 x Gasket Kit (27-94996T2)
- 1 x Hinge Pin Tool (91-78310/9178310)
- 4 x O-Rings
Installation Notes
- Disconnect the battery and trim the sterndrive to the trailer position.
- Remove the sterndrive unit from the gimbal housing.
- Detach the old exhaust, driveshaft, and shift cable bellows, noting clamp positions.
- Use the included hinge pin tool to assist in removing the old gimbal bearing.
- Thoroughly clean all mating surfaces, removing any old sealant or gasket material.
- Install the new gimbal bearing and ensure it is properly aligned.
- Install the new shift cable bellows, exhaust bellows, and driveshaft bellows with new clamps.
- Install the new gasket kit before reattaching components.
- Reinstall the sterndrive, verifying proper alignment and function.
- After reassembly, reconnect the battery and check for water leaks in a controlled environment.
Troubleshooting & FAQ
How do I know if this kit fits my sterndrive?
This kit is designed for MerCruiser Alpha One Gen 2 sterndrives from 1991 and newer, with serial numbers 0D469859 and higher. It is critical to verify your model and serial number before purchasing to ensure compatibility.
What are the signs that my transom seal needs replacement?
Common signs of failure include water visible inside the boat or within the bellows, a roaring or grinding noise from the gimbal bearing area (especially when turning), or increasing difficulty when shifting gears. Regular inspection is the best way to catch issues early.
How often should the bellows be replaced?
As a best practice for preventative maintenance, bellows should be inspected annually for cracks, drying, or damage and replaced every two years, regardless of visible condition, to prevent catastrophic failure.
Is the included gimbal bearing the greasable type?
Yes, this kit includes a greasable gimbal bearing (part 30-60792A4), which allows for periodic lubrication to extend its service life.
What is the Hinge Pin Tool used for?
The included Hinge Pin Tool (replaces 91-78310) is essential for removing and installing the hinge pins that connect the sterndrive to the bell housing. This tool simplifies a critical step of the transom service process.
Is this an OEM or an aftermarket part?
This listing is for an aftermarket replacement kit, not an OEM part. It is built to meet or exceed OEM-level specifications using comparable materials and manufactured in an ISO 9002 certified facility, with batch inspections for quality and consistency.
What are the shipping speed and cost?
We ship worldwide quickly, with typical transit times of 5–15 days for most regions. Standard shipping is free, and expedited options may be available at checkout depending on your location.
What is the warranty and return policy?
This kit is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. Please see our policy page or contact us 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 quality control.
Payment & Security
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