Gear Housing Seal Kit – Fits Mercury/Mariner 3.0L V6 200/225/250 HP (Replaces 26-816575A4)

$37.79 $60.00

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Gear Housing Seal Kit – Fits Mercury/Mariner 3.0L V6 200/225/250 HP (Replaces 26-816575A4) 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

This Gear Housing Seal Kit is engineered for Mercury and Mariner 3.0L V6 outboards, including 200, 225, and 250 HP models in EFI, Optimax, and DFI configurations. It provides all the necessary seals and gaskets to service the lower unit gearcase, preventing water intrusion and oil leaks to protect internal components.

It serves as a direct replacement for Mercury part 26-816575A4, Sierra 18-8382, and GLM 87512, offering a reliable alternative for gearcase maintenance and rebuilds.

Installs in the lower unit gearcase.
Specifically designed for models with a C-3 Casting gear housing.
Includes a comprehensive set of O-rings, oil seals, and gaskets for a complete service.

Part Number Matrix

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

Brand	Part Number
Mercury	26-816575A4
Sierra	18-8382
GLM	87512

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner models, compatibility is often determined by serial number range. This kit is primarily for 3.0L V6 engines with a C-3 Casting gear housing.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	V-200 3.0L EFI	200	2-Stroke	0T01000 and Up	26-816575A4
Mercury	V-200 Optimax 3.0L DFI	200	2-Stroke	0G386496 to 0G437999	26-816575A4	With C-3 Casting
Mercury	V-200 Optimax 3.0L DFI	200	2-Stroke	0G438000 - 1B504988	26-816575A4
Mercury	V-225 3.0L	225	2-Stroke	0D280813 - 0G437999	26-816575A4	With C-3 Casting
Mercury	V-225 3.0L	225	2-Stroke	0G438000 and Up	26-816575A4
Mercury	V-225 3.0L EFI	225	2-Stroke	0G129222 to 0G437999	26-816575A4	With C-3 Casting
Mercury	V-225 EFI	225	2-Stroke	0G438000 - 1B504988	26-816575A4
Mercury	V-225 Optimax 3.0L DFI	225	2-Stroke	0G590000 - 1B5049888	26-816575A4
Mercury	V-250 3.0L EFI	250	2-Stroke	0G129222 to 0G437999	26-816575A4	With C-3 Casting
Mercury	V-250 3.0L EFI	250	2-Stroke	0G438000 - 1B5049888	26-816575A4

Technical Specs

Product Type: Gear Housing Seal Kit
Installation: Lower Unit / Gearcase
Dimensions: 13.0 cm × 10.0 cm × 2.5 cm (approx. 5.1" × 3.9" × 1.0")
Weight: 0.059 kg (0.13 lb)
Note: For C-3 Casting gear housing
Thread Size: Multiple sizes for various seals
Warranty: 1 Year

What’s in the Box

1 x FACE SEAL V-RING (8M0110938)
1 x O-RING .796X .139 (25-21836)
1 x O-RING 1.046 X .139 (25-35027)
2 x O-RING .799 X .103 (25-896522)
1 x O-RING 3.850 X .210 (25-8M0110939)
1 x O-RING 2.175 X .103 (25-8M0110940)
1 x OIL SEAL (26-14077)
2 x OIL SEAL (26-66302)
1 x OIL SEAL (26-76868)
1 x OIL SEAL (26-8164641)
1 x DRAIN PLUG SEAL (26-830749)
1 x UPPER WTR PUMP GASKET (27-8172771)
1 x SHIFT SHAFT COVER GASKET (27-858935)
1 x GASKET FACEPLATE TO GEARCASE (27-8M0142162)

Installation Notes

Place the outboard in an upright, stable position and drain the gearcase oil into a suitable container.
Remove the propeller and disconnect the shift linkage. Unbolt and carefully remove the lower unit from the engine.
Disassemble the gearcase to access the driveshaft and propeller shaft carriers, bearings, and seals. Keep parts organized.
Carefully remove all old gaskets, O-rings, and oil seals from the housing, shafts, and carriers. Clean all sealing surfaces thoroughly.
Install the new seals and O-rings from the kit, applying a light coat of marine grease to help with seating and to prevent damage.
Reassemble the gearcase components according to the manufacturer's service manual, ensuring correct alignment and torque specifications.
Reinstall the lower unit, reconnect the shift linkage, and mount the propeller.
Refill the gearcase with the recommended marine gear lubricant. Install new drain plug seals and tighten securely.
After a brief run (on a water source), check for any signs of oil or water leaks around the seals.

Troubleshooting & FAQ

How do I know if this seal kit fits my engine?

Verify your engine model, HP, and serial number against the compatibility table. This kit is specifically intended for Mercury/Mariner 3.0L V6 models that use a C-3 Casting gear housing. If your model is listed, it is a confirmed fit.

What are the signs of a failing gear housing seal?

The most common sign is milky or cloudy gear lube, which indicates water has mixed with the oil. Other symptoms include visible oil leaks around the propeller shaft area, a persistent sheen of oil on the water, or finding excessive metal shavings on the magnetic drain plug.

How often should these seals be replaced?

It is recommended to replace gearcase seals during regular lower unit service, typically every 100-300 operating hours or at least once a season. You should replace them immediately if you notice any signs of leaks or water intrusion.

Is this kit the same as the Mercury OEM 26-816575A4?

This is an aftermarket kit designed to meet or exceed the performance of the OEM equivalent. It includes all the direct-replacement seals and gaskets required for a standard gear housing service, cross-referenced to the OEM part number.

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

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
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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