Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 (Replaces 30-803099T1)
Transom Seal Repair Kit – Fits MerCruiser Alpha One Gen 2 (Replaces 30-803099T1) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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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 (Replaces...
Product Details
This comprehensive Transom Seal Repair Kit is designed for MerCruiser Alpha One Generation 2 sterndrives manufactured from 1991 to the present (serial numbers 0D469859 and up). It provides all the essential bellows, gaskets, and bearings to perform a complete transom service, addressing common wear and leak points to restore a watertight seal and reliable operation.
This kit serves as a direct replacement for Mercury 30-803099T1, Sierra 18-8206-1, and Mallory 9-72904, offering a reliable and cost-effective alternative to OEM parts.
- Engineered for direct OEM replacement, ensuring proper fit and function.
- Bellows are made from high-quality marine-grade rubber with stainless steel clamps for durability.
- Includes a greasable gimbal bearing for extended service life.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 30-803099T1 |
| Sierra | 18-8206-1 |
| Mallory | 9-72904 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser sterndrives, this kit fits Alpha One Gen II models from 1991 to present with serial numbers 0D469859 and higher.
| 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 and up |
Technical Specs
- Product Type
- Transom Seal Repair Kit
- Installation
- Direct OEM replacement
- Housing Material
- Marine-grade rubber bellows with stainless steel clamps
- Housing Color
- Black
- Dimensions
- Shipping: 353mm × 213mm × 160mm (13.9" × 8.4" × 6.3")
- Weight
- 2.23 kg (4.9 lbs)
- Fitting Type
- Direct fit to MerCruiser Alpha One Gen 2
- Warranty
- Limited Lifetime (Sierra); OEM warranty (Mercury)
- Other Technical Attributes
- Includes greasable gimbal bearing
What’s in the Box
- 1 x Drive Shaft Bellows (816431A1)
- 1 x Exhaust Bellows Assembly (18654A1/8M0124227)
- 1 x U-Joint Bellows (74639A2)
- 1 x Gimbal Bearing Assembly (30-862540A3/30-879194A01/30-8M2010910)
- 1 x Water Inlet Hose (32-4172533/32-8M0062309/32-8M0062593)
- 1 x Outer Seal Kit (27-94996Q2/27-8M0091545)
Installation Notes
- Disconnect the boat's battery and trim the sterndrive to the full "up" position.
- Remove the sterndrive unit from the transom assembly according to manufacturer guidelines.
- Carefully remove the old U-joint, exhaust, and drive shaft bellows, along with their clamps.
- Extract the old gimbal bearing using an appropriate puller tool. Remove the water inlet hose and outer seals.
- Thoroughly clean all mating surfaces on the transom housing and bell housing, removing any old sealant or debris.
- Install the new gimbal bearing, ensuring it is properly seated and aligned.
- Fit the new bellows, water hose, and seals, securing them with the provided clamps. Ensure all connections are tight.
- Apply marine-grade grease to the U-joints and gimbal bearing through its grease fitting.
- Reinstall the sterndrive unit, ensuring correct alignment of the drive shaft.
- After installation, lower the drive and check for water leaks before operating the vessel.
Troubleshooting & FAQ
How do I know if this kit fits my sterndrive?
This kit is specifically for MerCruiser Alpha One Generation 2 sterndrives made from 1991 onwards, with a serial number of 0D469859 or higher. Please verify your drive model and serial number before ordering.
What are the signs my transom seals are failing?
Common symptoms include water in the bilge (especially after being in the water), a roaring or grinding noise from the gimbal bearing when turning, or visible cracks and deterioration of the rubber bellows.
Is the included gimbal bearing pre-greased?
The bearing has assembly grease but must be lubricated with marine-grade grease through its zerk fitting after installation and as part of your regular maintenance schedule.
What is the recommended replacement interval for these bellows?
As a general maintenance guideline, bellows should be inspected annually for cracks or wear and typically replaced every 3-5 years, depending on usage (freshwater vs. saltwater) and storage conditions.
Can I replace just one bellow instead of the whole kit?
While possible, it is highly recommended to replace all bellows, the gimbal bearing, and associated seals at the same time. These components wear at a similar rate, and replacing them together saves labor in the long run and ensures a complete, reliable repair.
What's the difference between this kit and an OEM part?
This is an aftermarket kit designed to meet or exceed original equipment manufacturer (OEM) specifications for fit, form, and function. It offers comparable performance and materials at a more competitive price point.
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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