Lower Unit Seal Kit – Fits Johnson/Evinrude 18-25 HP (Replaces 18-2684, 87606, 9-74105)
Lower Unit Seal Kit – Fits Johnson/Evinrude 18-25 HP (Replaces 18-2684, 87606, 9-74105) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
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Lower Unit Seal Kit – Fits Johnson/Evinrude 18-25 HP (Replaces 18-2...
Lower Unit Seal Kit – Fits Johnson/Evinrude 18-25 HP (Replaces 18-2684, 87606, 9-74105) is backordered and will ship as soon as it is back in stock.
Product Details
This Lower Unit Seal Kit – Fits Johnson/Evinrude 18-25 HP provides all necessary seals to service the lower unit gearcase on Johnson/Evinrude outboard motors. It is designed for 18 HP (1958–1973), 20 HP (1966–1973, 1979), and 25 HP (1969–1978) 2-Stroke models. The kit also fits select 6 HP outboards from 1967 ("S" suffix) and 1968 ("C" suffix).
This kit serves as a direct replacement for Sierra 18-2684, GLM 87606, and Mallory 9-74105.
- Replaces all essential OEM lower unit gearcase seals for a complete service.
- Suitable for both DIY and professional installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-2684 |
| GLM | 87606 |
| Mallory | 9-74105 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Johnson/Evinrude applications, pay close attention to the model year and any specific suffixes noted, as fitment can vary.
| Brand | Model | Rated HP | Stroke | Years | Notes |
|---|---|---|---|---|---|
| Johnson/Evinrude | Outboard | 6 | 2-Stroke | 1967 | "S" suffix only; Limited application |
| Johnson/Evinrude | Outboard | 6 | 2-Stroke | 1968 | "C" suffix only; Limited application |
| Johnson/Evinrude | Outboard | 18 | 2-Stroke | 1958–1973 | |
| Johnson/Evinrude | Outboard | 20 | 2-Stroke | 1966–1973, 1979 | |
| Johnson/Evinrude | Outboard | 25 | 2-Stroke | 1969–1978 |
Technical Specs
- Product Type
- Lower Unit Seal Kit
- Installation
- DIY/Professional
- Weight
- 0.05 lbs (0.023 kg)
- Other Technical Attributes
- Replaces OEM lower unit gearcase seals
What’s in the Box
- 1 x Shift Rod Gasket (304764/18-0882)
- 1 x Oil Seal (0321787/18-2031)
- 2 x Oil Seal (0321788/18-2032)
- 1 x Seal (309044/18-2534)
- 2 x Drain/Fill Plug Washer (311598/18-4248)
- 1 x O-Ring (301877/18-7100)
- 1 x O-Ring (307853/18-7120)
- 1 x O-Ring (321921/18-7411)
- 1 x O-Ring (302493/18-7112)
Installation Notes
- Place a drain pan under the lower unit and remove the drain/fill screws to empty the gear lube.
- Remove the propeller and disconnect the shift linkage. Unbolt and carefully lower the gearcase from the engine.
- Disassemble the gearcase components, including the propeller shaft housing and driveshaft bearing carrier, exposing the old seals.
- Carefully remove all old seals, O-rings, and gaskets, taking note of their orientation. Clean the sealing surfaces thoroughly.
- Lubricate the new seals with marine grease and press them into place using an appropriate seal driver or socket. Ensure they are seated correctly.
- Install the new gaskets and O-rings, reassembling the gearcase components in reverse order.
- Re-install the lower unit onto the engine, reconnect the shift linkage, and torque all bolts to the manufacturer's specification.
- Refill the gearcase with fresh lower unit lube from the bottom fill hole until it seeps out the top vent hole. Re-install both screws with new washers.
- After running the engine, check for any signs of water intrusion or oil leaks.
Troubleshooting & FAQ
What are the signs my lower unit seals are failing?
The most common sign of a failed seal is milky, creamy, or cloudy gear lube, which indicates water has entered the gearcase. You may also notice oil leaking from around the propeller shaft or dripping from the skeg.
How can I confirm this kit fits my engine?
Please check the "Engine & Model Compatibility" table. For the 6 HP models, it is essential to match both the year and the specific model suffix ("S" for 1967, "C" for 1968), as fitment is limited.
How often should I replace lower unit seals?
It is recommended to inspect your gear lube annually for water intrusion. Seals should be replaced every 3-5 years as preventative maintenance, or immediately if you detect a leak or water in the oil.
Does this kit include every seal in the lower unit?
This kit contains the most commonly replaced seals for a standard lower unit service, as detailed in the "What’s in the Box" section. For a complete overhaul, you may need additional parts. Always compare the included parts with your unit's requirements.
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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