Mercury – Gear Case Drain Screw Seal (Pack of 2) | Gearcase Hardware | Rubber-Coated Stainless Steel | 8M0058391

Overview

When you’ve spent enough time on the water, you start to appreciate the small parts that keep everything running smoothly. They’re easy to overlook, but they’re also the ones that protect your gear when you’re miles from shore or backing away from the dock on a quiet morning. The Mercury Gear Case Drain Screw Seal is one of those little essentials that gives you real peace of mind. It keeps water out, keeps gear lube in, and helps your lower unit stay healthy season after season. Simple, reliable, and absolutely necessary — it’s the kind of part that seasoned boaters always keep spares of.

Key Features

• Rubber-coated Stainless Steel seal for durable, reliable gearcase protection
• Designed for 3/8-16 drain and fill screw holes
• Helps prevent water intrusion and gear lube leakage
• Protects against catastrophic gearcase damage caused by failed sealing
• Pack includes 2 seals
• Built to Mercury Marine OEM specifications for exact fit and long service life
• Mercury Marine part number 8M0058391

Engine & Boat Compatibility

• Fits most Mercury and Mariner outboards that use 3/8-16 drain/fill screws
• Compatible with all MerCruiser sterndrives requiring this seal size
• Suitable for fishing boats, center consoles, pontoons, bowriders, sport boats, and cruisers
• Works with a wide range of horsepower levels when the gearcase uses the 3/8-16 screw design

Performance & Practical Benefits

What boaters appreciate most about this seal is how quietly it does its job. Once you seat the drain screw with a fresh washer, you know the lower unit is secure, tight, and protected against the one thing every boater fears: water inside the gearcase. Even a small amount can whip the oil into a milky mess, strip the gears of lubrication, and lead to severe — and expensive — internal damage.

The rubber-coated Stainless Steel construction gives the seal the perfect balance of resilience and flexibility. It compresses just enough to create a watertight bond, yet it’s strong enough to hold its shape under pressure and temperature swings. That means a smooth, secure fit every time you service your gear lube.

You’ll also feel peace of mind knowing you’ve installed a part built to Mercury’s precise OEM standards. It’s a perfect fit — no gaps, no compromises, no guessing. Just a clean seal that protects your investment. And because the pack includes two, you always have a spare ready for the next service, which beats scrambling to find one when the old washer falls or gets damaged during removal.

On the water, the benefit is simple: a gearcase that stays cool, lubricated, and steady. No whine, no grinding, no unexpected surprises. Just smooth, dependable performance.

Why Buy OEM

A genuine Mercury Marine part isn’t just a washer — it’s insurance. You’re choosing a seal engineered specifically for Mercury and MerCruiser gearcases, tested in real conditions, and trusted by boaters who expect reliability. Aftermarket washers often use cheaper metal, inconsistent thickness, or poor coatings that don’t seal properly. With OEM, you eliminate the risk. It’s cost-effective, dependable, and designed to work right the first time. That’s the kind of advice any experienced boater would pass along.

FAQ

Q1: Which systems does this seal fit?

It fits Mercury and Mariner outboards and all MerCruiser sterndrives that use a 3/8-16 drain/fill screw.

Q2: What makes it better than aftermarket versions?

OEM seals offer consistent thickness, superior coating, and proper fitment to prevent leaks and water intrusion.

Q3: How do I know if this is the correct replacement?

If your gearcase uses a 3/8-16 drain screw, this is the correct seal. Refer to your manual if unsure.

Q4: Can it be used in both saltwater and freshwater?

Yes — the rubber-coated Stainless Steel design resists corrosion and maintains a tight seal in any environment.

Q5: Is installation straightforward?

Very. Remove the old washer, place a new one on the drain screw, and tighten securely to spec.