Gearcase Oil Seal for OMC – Replaces Sierra 18-2028 and OMC 318973

Product Details

This Gearcase Oil Seal for OMC is a single aftermarket replacement seal for compatible OMC marine gearcase and lower-unit applications. It is intended to help maintain the oil barrier at the sealing location and reduce the risk of gearcase lubricant leakage when installed correctly.

Catalog evidence identifies Sierra 18-2028 as a replacement reference for OMC 318973. Confirm the original part number, seal dimensions, and engine or gearcase service information before ordering.

• Single oil seal for compatible gearcase applications
• Aftermarket replacement component
• For OMC marine gearcase and lower-unit service where the listed reference applies
• Sold as one piece

Part Number Matrix

Use the following verified replacement references to compare the removed seal with this aftermarket component.

Engine & Model Compatibility

This seal is intended for OMC marine gearcase or lower-unit applications that use OMC 318973 or the corresponding Sierra 18-2028 replacement. A complete model, year, horsepower, stroke, shaft, and serial-number fitment range was not established in the available catalog records.

Technical Specs

Part Type

Gearcase oil seal

Application

Compatible OMC marine gearcase or lower-unit service

Replacement References

Sierra 18-2028; OMC 318973

Quantity

1 piece

Product Type

Single replacement component; not a kit

What's in the Box

• 1 × Gearcase oil seal

Installation Notes

1. Drain the gearcase oil as directed by the applicable service manual and clean the seal area of oil, sealant, and debris.
2. Remove the old seal using a suitable seal-removal method that will not damage the housing, shaft, or adjacent components.
3. Inspect the shaft and seal bore for scoring, corrosion, burrs, or wear. Correct any condition that could prevent proper sealing.
4. Compare the replacement seal with the removed part for configuration and dimensions before installation.
5. Lubricate the seal lip with the lubricant specified for the application, unless the service manual directs otherwise.
6. Install the seal squarely with an appropriately sized seal driver. Avoid striking the sealing lip or cocking the seal in the housing.
7. Seat the seal to the depth specified by the applicable manufacturer service information.
8. Refill the gearcase with the recommended lubricant and quantity, then inspect for leaks after initial operation.

Troubleshooting & FAQ

How do I know if the gearcase seal needs replacement?

Possible signs include lubricant leaking from the lower unit, milky gearcase oil indicating water contamination, or a falling lubricant level between service intervals. Inspect the shaft, housing, and related seals during diagnosis because a leak may originate from another location.

Can I reuse an old seal during reassembly?

No. A removed oil seal should normally be replaced rather than reused, since removal can damage the sealing lip or distort the seal body.

What causes premature seal failure?

Shaft scoring, corrosion, incorrect installation depth, contamination, a damaged housing, incompatible lubricant, or operating the gearcase with insufficient lubricant can contribute to early failure.

Will this seal fit all OMC models?

No universal OMC fitment claim is made. The available reference identifies OMC 318973 and Sierra 18-2028, but model, year, serial-number, and exact installation-position conditions should be confirmed with the engine or gearcase service manual.

Do I need special tools to install this seal?

A suitable seal driver is recommended for even, square installation. An appropriately sized socket may be used only when it contacts the seal's intended driving surface and does not damage the sealing lip or housing.

What lubricant should I use after installation?

Use the gearcase lubricant type, viscosity, and fill procedure specified in the applicable engine or gearcase service manual.

Is this an OEM component?

No. This listing is for an aftermarket replacement oil seal. Sierra 18-2028 and OMC 318973 are reference numbers used for identification and cross-reference purposes.

What is included with the purchase?

The package contains one gearcase oil seal. No additional seals, gaskets, keys, hardware, or installation tools are included unless separately stated.

Safety & Important Info

• Verify the original part number, dimensions, seal orientation, and installation position before ordering.
• Do not rely on a general OMC brand match alone; model, serial-number, and gearcase configuration may affect fitment.
• Use the applicable service manual for lubricant specifications, installation depth, and torque requirements.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended when servicing the lower unit or when specialized tools are required.

About Sea Sierra

• Marine replacement components selected for practical service applications.
• Clear part-number cross-references to help customers compare replacement options.
• Support focused on accurate identification and responsible installation.