Lower Unit Oil Drain Plug – Fits Mercury/Mercruiser 40-115 HP (Replaces 10-79953Q2, 10-79953A2, 18-2244)
Lower Unit Oil Drain Plug – Fits Mercury/Mercruiser 40-115 HP (Replaces 10-79953Q2, 10-79953A2, 18-2244) 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
Lower Unit Oil Drain Plug – Fits Mercury/Mercruiser 40-115 HP (Repl...
Product Details
This Marine Lower Unit Oil Drain Plug is a direct-fit replacement for a range of Mercury and Mercruiser outboard engines and stern drives. It is designed for 40-115 HP outboards as well as Bravo and Alpha One Gen 2 stern drive models, providing a reliable seal for your gearcase.
It serves as a direct cross-reference for multiple manufacturer part numbers, including Mercury 10-79953Q2, 10-79953A2, Sierra 18-2244, GLM 22420, and Mallory 9-72650.
- Installs as a direct replacement screw with gasket.
- Constructed from durable, non-magnetic stainless steel for corrosion resistance.
- Includes two plugs and two gasket seals for a complete service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 10-79953Q2 |
| Mercury | 10-79953A2 |
| Mercury | 10-79953Q04 |
| Mercury | 10-79953 |
| Mercury | 79953Q04 |
| Sierra | 18-2244 |
| GLM | 22420 |
| Mallory | 9-72650 |
| Easterner | C14406 |
| WSM | 607-14 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Compatibility is confirmed for the following Mercury/Mercruiser engines. Please verify that your specific model and year are covered before purchase.
| Brand | Model | Rated HP | OEM Part No. |
|---|---|---|---|
| Mercury | Outboard | 40 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 50 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 60 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 70 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 75 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 90 | 10-79953Q2/10-79953A2 |
| Mercury | Outboard | 115 | 10-79953Q2/10-79953A2 |
| Mercruiser | Bravo | 10-79953Q2/10-79953A2 | |
| Mercruiser | Alpha One Gen 2 | 10-79953Q2/10-79953A2 |
Technical Specs
- Product Type
- Lower Unit Oil Drain Plug
- Installation
- Direct Replacement Screw with Gasket
- Connection
- 3/8-16 Thread
- Housing Material
- Stainless Steel
- Housing Color
- Silver
- Fitting Type
- Screw with Gasket
- Thread Size
- 3/8-16
- Other Technical Attributes
- Non-magnetic design
What’s in the Box
- 2 x Lower Unit Oil Drain Plug (10-79953Q2)
- 2 x Gasket Seals
Installation Notes
- Position a suitable drain pan under the lower unit's gearcase.
- Remove both the upper (vent) and lower (drain) plugs using a large flathead screwdriver.
- Allow the gear oil to drain completely. Inspect the old oil for any metal shavings or milky appearance, which can indicate internal wear or water intrusion.
- Clean the plug threads on the gearcase.
- Install the new drain plug with its gasket in the lower hole. Hand-tighten, then snug it firmly with a screwdriver. Do not overtighten.
- Slowly pump new marine gear lubricant into the lower hole until it flows out of the upper vent hole.
- Install the new vent plug with its gasket in the upper hole, then quickly remove the lube pump and reinstall the lower drain plug.
- Wipe the gearcase clean and check for leaks after a few minutes.
Troubleshooting & FAQ
How do I confirm this plug fits my engine?
This plug is designed for Mercury/Mercruiser engines in the 40-115 HP range and Bravo/Alpha One Gen 2 stern drives. The most reliable method is to match your original part number to the ones listed in our Part Number Matrix. Also, verify the 3/8-16 thread size.
Why is a non-magnetic plug specified?
While some drain plugs are magnetic to capture metallic debris, this non-magnetic stainless steel version is designed to OEM specifications for models where this feature was not standard. It offers superior corrosion resistance in saltwater environments.
What are the signs of a faulty drain plug or gasket?
Signs include visible gear oil leaks around the plug, difficulty in tightening the plug (stripped threads), or a cracked/brittle gasket seal. Any of these warrant immediate replacement to prevent water intrusion or oil loss.
How often should I replace the drain plug gaskets?
It is best practice to replace the drain plug gaskets every time you change your gear oil, which is typically recommended annually or every 100 hours of operation, whichever comes first. This kit includes new gaskets.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It has been built to OEM-level specifications with comparable materials. All parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
What are the shipping speed & cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free, with expedited options appearing at checkout where available.
What is the warranty & return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement part, not an OEM component.
- Professional installation is recommended for safety and optimal performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — Enjoy free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — We offer fair pricing without compromising on materials or quality control.
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.
