Lower Unit Seal Kit – Fits Yamaha F20/F25 4-Stroke Outboards (Replaces 65W-W0001-20-00)
Lower Unit Seal Kit – Fits Yamaha F20/F25 4-Stroke Outboards (Replaces 65W-W0001-20-00) is backordered and will ship as soon as it is back in stock.
Couldn't load pickup availability
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 is a complete Lower Unit Seal Kit designed for Yamaha F20, F25, T25, and FT25 4-stroke outboard models manufactured between 1998 and 2008. It provides all the necessary seals to service the lower unit driveshaft and propeller shaft, preventing water intrusion and gear oil leaks.
This kit serves as a direct replacement for OEM part number 65W-W0001-20-00 and aftermarket equivalent Sierra 18-99073.
- Provides a direct OEM-equivalent installation.
- Restores sealing integrity for driveshaft and lower unit components.
- Engineered for marine environments.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 65W-W0001-20-00 |
| Sierra | 18-99073 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is a confirmed fit for a range of Yamaha 4-stroke outboards from 20 to 25 HP produced between 1998 and 2008.
It is also listed as compatible with select Parsun and Mercury/Mariner models, though specific year ranges should be verified with your service manual.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F20 | 20 | 4-Stroke | 1998–2008 | 65W-W0001-20-00 | |
| Yamaha | F25 | 25 | 4-Stroke | 1998–2008 | 65W-W0001-20-00 | |
| Yamaha | T25 | 25 | 4-Stroke | 1998–2008 | 65W-W0001-20-00 | |
| Yamaha | FT25 | 25 | 4-Stroke | 1998–2008 | 65W-W0001-20-00 | |
| Parsun | F20 | 20 | 4-Stroke | Compatible per BHMarine | ||
| Parsun | F25 | 25 | 4-Stroke | Compatible per BHMarine | ||
| Mercury | F20 | 20 | 4-Stroke | Compatible per BHMarine | ||
| Mercury | F25 | 25 | 4-Stroke | Compatible per BHMarine | ||
| Mariner | F20 | 20 | 4-Stroke | Compatible per BHMarine | ||
| Mariner | F25 | 25 | 4-Stroke | Compatible per BHMarine |
Technical Specs
- Product Type
- Lower Unit Seal Kit
- Installation
- OEM replacement
- Dimensions
- 16.0" L x 9.0" W x 1.0" H
- Other Technical Attributes
- Seal kit for driveshaft and lower unit components
What’s in the Box
- 1 x Lower Unit Seal Kit (Replaces Yamaha 65W-W0001-20-00)
Installation Notes
- Place a drain pan under the lower unit and remove the drain and vent screws to drain the gearcase oil completely.
- Remove the propeller assembly.
- Unbolt and carefully slide the lower unit off the engine's driveshaft housing.
- Using an appropriate seal puller, remove the old propeller shaft and driveshaft seals. Be cautious not to scratch the housing surfaces.
- Thoroughly clean the seal seating areas and inspect the shafts for any scoring, rust, or fishing line debris. Polish any minor imperfections.
- Lubricate the new seals with marine grease.
- Using a seal driver or a socket of the correct diameter, gently and evenly press the new seals into place until they are fully seated.
- Lightly grease the driveshaft splines and propeller shaft.
- Reinstall the lower unit, ensuring the driveshaft, shift shaft, and water tube align correctly. Torque bolts to manufacturer specifications.
- Reinstall the propeller.
- Refill the lower unit with the recommended marine gear lubricant through the bottom drain hole until it flows out of the top vent hole.
- Reinstall the vent and drain screw gaskets and screws. Check for leaks after a short period.
Troubleshooting & FAQ
How do I know if my lower unit seals are failing?
The most common sign is milky or cloudy gearcase oil, which indicates water has mixed with the oil. You may also notice gear oil leaking from around the propeller shaft or onto the ground beneath the skeg.
Can this kit be used for models outside the specified 1998–2008 year range?
This kit is specifically designed for the Yamaha F20/F25 engines listed from 1998–2008. Using it on other years is not recommended, as part numbers and seal dimensions can vary. Always verify the part number for your specific engine model and year.
What causes lower unit seals to fail?
The most frequent cause of failure is age and normal wear. However, damage from fishing line wrapped around the propeller shaft is also very common, as it can cut into the seal and create a leak path. Scored or corroded shafts can also accelerate seal wear.
Do I need special tools for installation?
While basic mechanical work can be done with standard tools, using a dedicated seal puller and a proper seal driver set is highly recommended. These tools help prevent damage to the gearcase housing and ensure the new seals are installed straight and to the correct depth.
Is it necessary to replace all seals at once?
Yes. If one seal has failed due to age, the others are likely near the end of their service life. Replacing them all as a set is best practice to ensure a reliable, long-lasting repair and prevent having to disassemble the unit again soon.
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
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
