Gearcase Seal Kit – Fits Yamaha 25/30HP (Replaces 6J8-W0001-21-00, 6J8-W0001-C2-00)
Gearcase Seal Kit – Fits Yamaha 25/30HP (Replaces 6J8-W0001-21-00, 6J8-W0001-C2-00) 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
Product Details
This aftermarket Gearcase Seal Kit – Fits Yamaha 25/30HP is designed to restore the integrity of the lower unit on Yamaha 25HP 2-Stroke (1997–2002) and 30HP 2-Stroke (1987–up) outboard engines. It provides all necessary seals to prevent water intrusion and lubricant leakage, ensuring reliable performance.
It serves as a direct replacement for Sierra part 18-2789 and Yamaha OEM parts 6J8-W0001-21-00, 6J8-W0001-C2-00, 6J8-W0001-20-00, and 6J8-W0001-22-00.
- Installs in the lower unit/gearcase.
- Engineered as a direct OEM-equivalent replacement.
- Contains seals required for a standard rebuild.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 6J8-W0001-C2-00 | Current OEM part number. |
| Yamaha | 6J8-W0001-21-00 | Superseded by 6J8-W0001-C2-00. |
| Yamaha | 6J8-W0001-22-00 | Alternate superseded part number. |
| Yamaha | 6J8-W0001-20-00 | Alternate superseded part number. |
| Sierra | 18-2789 | Aftermarket equivalent. |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | C25 | 25 | 2-Stroke | 1997–2002 | 6J8-W0001-C2-00 | Supersedes 6J8-W0001-21-00 |
| Yamaha | 30HP | 30 | 2-Stroke | 1987–up | 6J8-W0001-C2-00 | Supersedes 6J8-W0001-21-00 |
Technical Specs
- Product Type
- Gearcase/Lower Unit Seal Kit
- Installation
- Lower Unit/Gearcase
- Dimensions
- 13.0" x 10.0" x 0.38"
- Other Technical Attributes
- OEM equivalent replacement
What’s in the Box
- 1 x Gearcase Seal Kit (Replaces 6J8-W0001-C2-00)
Installation Notes
- Begin by draining the gearcase lubricant completely into an approved container.
- Carefully remove the lower unit (gearcase) from the outboard's midsection.
- Disassemble the gearcase to access the old seals, noting the order and orientation of each component.
- Thoroughly clean all parts and mating surfaces, removing any old gasket material or sealant residue.
- Install the new seals from the kit, lightly lubricating them with marine grease to ensure proper seating and prevent damage.
- Reassemble the gearcase components, torquing fasteners to the manufacturer's recommended specifications.
- Re-install the lower unit and refill with the correct type and amount of fresh gear lube before operation.
Troubleshooting & FAQ
How do I know if my gearcase seals are failing?
Common signs include milky or discolored gear lube (indicating water intrusion) or visible lubricant leaks around the propeller shaft, driveshaft, or drain screws. A pressure test of the gearcase can definitively confirm a leak.
Will this kit fit my Yamaha 30HP model from 1989?
Yes, this kit is specified to fit all Yamaha 30HP 2-Stroke engines manufactured from 1987-up, which includes your 1989 model.
Does this kit include both driveshaft and propeller shaft seals?
Yes, this is a comprehensive gearcase seal kit that includes the necessary seals for a standard lower unit service, covering both the driveshaft and propeller shaft areas. Always compare the new parts to your old ones before installing.
What is the difference between part 6J8-W0001-21-00 and 6J8-W0001-C2-00?
Part number 6J8-W0001-C2-00 is the direct supersession for 6J8-W0001-21-00. They are functionally identical, with the C2-00 being the later, updated revision from the manufacturer. Our kit is a replacement for both.
What are the signs of a bad seal besides leaks?
Aside from visible leaks, you might notice grinding noises from the lower unit, excessive heat, or metal shavings on the magnetic drain plug, which can result from component failure caused by water-contaminated lubricant.
How often should gearcase seals be replaced?
There is no fixed replacement interval, but seals should be inspected during every lower unit service (e.g., water pump replacement) and replaced immediately if there are any signs of leaks, damage, or water intrusion in the gear lube.
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.
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