Transom Seal Kit – Fits MerCruiser R/MR/Alpha One Gen I Stern Drives (Replaces 30-803098T1)
Transom Seal Kit – Fits MerCruiser R/MR/Alpha One Gen I Stern Drives (Replaces 30-803098T1) 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 Kit – Fits MerCruiser R/MR/Alpha One Gen I Stern Drive...
Product Details
This Transom Seal Kit – Fits MerCruiser R/MR/Alpha One Gen I Stern Drives (Replaces 30-803098T1) is designed for MerCruiser R, MR, and Alpha One Generation I stern drives produced from 1983–1991 (serial numbers 6225577 through 0D469858). The kit provides all essential components to reseal the transom assembly, preventing water intrusion and ensuring reliable operation.
It serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury Marine 30-803098T1, Sierra 18-8205, Sierra 18-8217, GLM 21951, Mallory 9-72901, and Redline RL8205.
- Engineered for direct replacement and installation.
- Includes a heavy-duty gimbal bearing, bellows, gaskets, and all required hardware.
- Specifically designed for use with an exhaust tube configuration.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| Mercury Marine | 30-803098T1 |
| Sierra | 18-8205 |
| Sierra | 18-8217 |
| GLM | 21951 |
| Mallory | 9-72901 |
| Redline | RL8205 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure accurate fitment.
This kit is compatible with the following MerCruiser stern drive and transom assemblies.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | R/MR/Alpha One (Sterndrive) | 4-Stroke | 1983–1991 | 30-803098T1 | Serial #s: 6225577-0D469858 | |
| MerCruiser | R/MR/Alpha One (Transom Assembly) | 4-Stroke | 1983–1991 | 30-803098T1 | Serial #s: 6216687-0D469858 |
Technical Specs
- Product Type
- Transom Seal Kit
- Installation
- Direct replacement
- Housing Material
- Rubber, metal, plastic
- Housing Color
- Black
- Other Technical Attributes
- For use with exhaust tube configuration
What’s in the Box
- 1 x Heavy Duty Gimbal Bearing (18-2100 / 30-60794A4)
- 1 x U-Joint Bellows (18-2751 / 60932A4)
- 1 x Exhaust Tube (18-2760 / 78458A1)
- 1 x Water Intake Hose (18-3601 / 32-32461)
- 1 x Water Intake Hose (18-3602 / 32-41725-33)
- 1 x Outdrive Mounting Gasket (18-2743 / 27-94996-2)
- 2 x Bell Housing Gasket (18-2840 / 27-35982)
- 1 x O-Ring (18-7153 / 25-25439)
- 1 x O-Ring (18-7117 / 25-35027)
- 2 x Hose Clamp (18-7310 / NSS)
- 1 x O-Ring (18-7170 / 25-33504)
- 1 x Hose Clamp (18-7312 / NSS)
- 1 x Shift Cable Bellows (18-2753-1 or 18-2753-2 / 74639)
- 1 x Bellows Clamp (18-7321 / 54-38863)
Installation Notes
A notable feature of this kit is its exhaust tube configuration. It is designed for use with a single hose clamp on the transom side, which may produce a slightly louder exhaust sound compared to the original OEM setup that used clamps on both ends.
- Disconnect the vessel's battery and all related power sources.
- Remove the stern drive unit from the transom assembly according to the manufacturer's service manual.
- Carefully detach and remove the old U-joint bellows, exhaust bellows, shift cable bellows, and gimbal bearing.
- Thoroughly clean all mating surfaces on the transom and bell housing, removing any old sealant or gasket residue.
- Press the new gimbal bearing squarely into the gimbal housing.
- Install the new exhaust tube, bellows, and water hoses using the provided gaskets, O-rings, and clamps.
- Ensure all bellows are properly seated and secured to create a watertight seal.
- Reinstall the outdrive, torquing fasteners to the manufacturer’s specifications.
- Reconnect the battery, start the engine, and meticulously check for any signs of water leaks around the transom assembly.
Troubleshooting & FAQ
How do I confirm this kit fits my MerCruiser stern drive?
This kit is specifically for MerCruiser R, MR, and Alpha One Generation I models from 1983 to 1991. The most reliable way to confirm fitment is to match your unit's serial number to the ranges listed: 6225577–0D469858 for sterndrives and 6216687–0D469858 for transom assemblies. Always cross-reference with the OEM part number 30-803098T1.
Is this transom seal kit different from the OEM version?
Our kit is built to meet or exceed OEM specifications for fit and function. However, there is one minor difference to note: this kit's exhaust tube is designed for a single hose clamp on the transom side. This may result in a slightly louder exhaust note than the original dual-clamp setup but does not affect performance or sealing.
What are the common signs that a transom seal kit needs to be replaced?
The most critical sign is water inside the boat's bilge, especially near the transom. Other indicators include visible cracks, drying, or rotting on the bellows; a noisy or rough-feeling gimbal bearing when turning the drive; or difficulty shifting, which could point to a leak in the shift cable bellows.
How often should bellows and seals be replaced?
As a general maintenance guideline, bellows and seals should be inspected annually and typically replaced every 3–5 years, depending on usage (saltwater vs. freshwater) and storage conditions. Proactive replacement is key to preventing catastrophic water intrusion.
Do I need special tools for installation?
Yes, replacing a transom seal kit typically requires specialized tools, including a gimbal bearing puller/installer, a bellows expander tool, and a hinge pin tool. We strongly recommend professional installation if you do not have these tools or experience with stern drive service.
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 and specifications against 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.
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