22-8M0058389 Gearbox Drain & Fill Screw Kit for Mercury MerCruiser | JLM Marine

Gearbox Drain & Fill Screw Kit for Mercury MerCruiser | JLM Marine

This Gearbox Drain & Fill Screw Kit is designed for use with 3/8 - 16 drain and fill hole screws on all MerCruiser stern drives, Mercury and Mariner outboards (except the Verado series). Engineered to help prevent gear lube from leaking out and water from seeping into the gear case, this kit plays a critical role in protecting your lower unit from serious damage.

Direct Replacements: 10-79953Q04, 22-8M0058389

• Includes 1 magnetic drain screw, 1 standard fill screw, and 2 new design yellow washer seals
• High-performance design ensures reliable sealing and easy maintenance
• Broad cross-reference compatibility with OEM and aftermarket brands

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

This kit is compatible with all MerCruiser stern drives, Mercury and Mariner outboards (except the Verado series) that use 3/8 - 16 drain and fill hole screws.

Technical Specifications

Package Contents

• 1 × Magnetic Drain Screw
• 1 × Standard Fill Screw
• 2 × New Design Yellow Washer Seals

Installation Guide

1. Position the boat so the lower unit is accessible and the engine has cooled completely. Gather the new drain screw, fill screw, and yellow washer seals from the kit.
2. Place a suitable drain pan beneath the lower unit to catch gear lube. Carefully remove the existing drain screw and allow all old lube to fully drain.
3. Once drained, clean the drain hole threads and inspect for debris or damage. Install the new yellow washer seal onto the new magnetic drain screw.
4. Thread the magnetic drain screw (with washer) into the drain hole by hand first to avoid cross-threading. Tighten to manufacturer's torque specification using a socket or wrench.
5. Locate the fill hole and remove the existing fill screw. Install the new yellow washer seal onto the new standard fill screw.
6. Using a suitable gear lube pump, slowly refill the lower unit with the correct type and quantity of gear oil until it begins to flow from the fill hole. Thread the fill screw (with washer) in by hand, then tighten to specification.
7. Wipe away any spilled lube and inspect both screws to confirm they are seated properly and not leaking. Dispose of old lube and washers according to local regulations.
8. Run the engine briefly in a test tank or on the water and re-check both screws for any signs of leakage. Top off gear lube if necessary.

Troubleshooting & FAQ

How do I confirm this kit fits my lower unit?
Verify that your MerCruiser stern drive, Mercury, or Mariner outboard (excluding Verado) uses 3/8 - 16 drain and fill screws. Cross-reference your existing part numbers with the table above or consult your engine's parts diagram.

What is the difference between the magnetic drain screw and the standard fill screw?
The magnetic drain screw attracts and captures metal particles that circulate in the gear lube, helping to identify wear or damage early. The standard fill screw seals the upper fill hole and does not have a magnet.

How often should I replace the washer seals?
Replace the yellow washer seals every time you remove the drain or fill screws during gear oil changes. Reusing old washers can lead to leaks and water intrusion.

Why is gear lube leaking from the drain screw after installation?
Ensure the yellow washer seal is properly seated on the screw and that the screw is tightened to the correct torque specification. If leakage persists, inspect the drain hole threads for damage or debris.

Can I use this kit on a Verado outboard?
No, this kit is not compatible with Mercury Verado series outboards. Verado models use a different drain and fill screw design.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.