Lower Unit Drain Plug Gaskets – Fits Mercury/Mariner & MerCruiser (Replaces 12-19183, 12-19183Q02)

$14.99

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Lower Unit Drain Plug Gaskets – Fits Mercury/Mariner & MerCruiser (Replaces 12-19183, 12-19183Q02) is backordered and will ship as soon as it is back in stock.

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

These Lower Unit Drain Plug Gaskets are designed for Mercury/Mariner outboard engines and MerCruiser sterndrives that use 3/8-16 drain and fill screw holes. They are essential for creating a tight seal during gear oil changes, preventing leaks and protecting your engine's lower unit. These high-quality gaskets fit a wide range of 4-stroke and select 2-stroke models.

This part serves as a direct interchange for multiple OEM and aftermarket part numbers, including Mercury 12-19183-3, 12-19183Q02, 12-19183K02, Sierra 18-2244, Mallory 9-60101, and GLM 31170.

Installation Fitment: Designed specifically for 3/8-16 UNC drain and fill screw holes.
Single-Use Design: For optimal performance and a leak-free seal, each gasket should be replaced with every gear oil change.
Durable Material: Constructed from a robust, asbestos-free rubber and plastic composite for long-lasting reliability.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury	12-19183-3
Mercury	12-19183Q02
Mercury	12-19183K02
Sierra	18-2244
Sierra	18-2245
SEI Marine	98-102-09
Mallory	9-60101
Mallory	9-60102
GLM	31170
OBR Red Rhino	MR-103

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner and MerCruiser models, these gaskets are broadly compatible with most engines of non-Japanese origin that feature the standard 3/8-16 drain and fill screws.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Mercury	All MerCruiser sterndrives	Various	4-Stroke	12-19183-3	With 3/8-16 drain/fill screw holes
Mercury/Mariner	Most non-Japanese origin outboards	Various	4-Stroke	12-19183-3	3/8-16 drain/fill screw

Technical Specs

Product Type: Lower Unit Drain Plug Gasket/Seal
Installation: Fits 3/8-16 drain/fill screw holes
Material: Asbestos-free rubber/plastic composite
Color: Black or Blue (varies by manufacturer)
Package Quantity: Multiple (10, 12, 20, or 30 pcs depending on brand)
Usage: One-time use; replace with each oil change
Replacement Frequency: With every gear oil change
Application: Mercury/Mariner outboards and MerCruiser sterndrives with 3/8-16 drain/fill holes

What’s in the Box

10 x Lower Unit Drain Plug Gaskets (JLM Marine variant)
12 x Lower Unit Drain Plug Gaskets (GHOONEY variant)
20 x Lower Unit Drain Plug Gaskets (GHmarine variant)
30 x Lower Unit Drain Plug Gaskets (BOLEWIN variant)

Installation Notes

Ensure the engine is turned off and has cooled down completely. Place a suitable drain pan below the lower unit's drain screw.
Carefully remove the lower magnetic drain plug screw, followed by the upper-level vent screw.
Allow the gear lube to drain fully. Inspect the drain screw's magnetic tip for any unusual metal filings.
Clean the drain screw threads thoroughly. Remove the old gasket and discard it.
Install the new drain plug gasket onto the screw.
Begin refilling the lower unit with the manufacturer-specified gear lube through the bottom drain hole.
Continue filling until you see a steady stream of new fluid emerge from the upper vent hole.
Re-install the top vent screw first to create a vacuum, then quickly re-install the lower drain screw with the new gasket.
Tighten both screws to the manufacturer's recommended torque specification. Do not overtighten, as this can damage the gearcase.
Wipe the area clean and monitor for any signs of leakage.

Troubleshooting & FAQ

How do I confirm these gaskets fit my exact engine model?

The best way to confirm fitment is by matching your old gasket's part number to the numbers listed in our Part Number Matrix. These gaskets are designed for any Mercury/Mariner or MerCruiser unit with 3/8-16 drain screw threads.

Can I re-use my old drain plug gasket?

No. These gaskets are designed for single use. They compress and deform to create a perfect seal. Re-using a gasket significantly increases the risk of a gear oil leak, which can lead to catastrophic lower unit failure.

The new gasket is a different color than my original. Is that okay?

Yes. The color (typically black or blue) varies by manufacturer and does not affect the function, fit, or material quality of the gasket. As long as the dimensions and application match, it is safe to use.

What are the signs of a failing drain screw gasket?

Common signs include a visible drip or film of gear oil on the skeg or around the drain screw, a rainbow sheen on the water near your lower unit, or a consistently low gear lube level. Replace the gasket immediately if you notice any of these signs.

What happens if I overtighten the drain screw?

Overtightening the drain screw can crack the gearcase housing or strip the threads, leading to very expensive repairs. It can also excessively flatten the gasket, causing it to fail. Always use a torque wrench and follow the manufacturer's specified torque values.

Why is it important to replace the gasket with every oil change?

Replacing the gasket with each gear lube service ensures a fresh, reliable seal. The old gasket has already been compressed and has likely hardened from heat cycles, making it less effective and prone to leaking. It is a cheap and critical preventative maintenance step.

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

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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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