Lower Gear Case Seal Kit – Fits Volvo Penta SX & OMC Cobra Sterndrives (Replaces 3855275, 0778351)
Lower Gear Case Seal Kit – Fits Volvo Penta SX & OMC Cobra Sterndrives (Replaces 3855275, 0778351) is backordered and will ship as soon as it is back in stock.
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Lower Gear Case Seal Kit – Fits Volvo Penta SX & OMC Cobra Ster...
Product Details
This Lower Gear Case Seal Kit provides the essential components for resealing the lower unit on Volvo Penta SX and OMC Cobra SX sterndrives. It is designed for a broad range of gasoline engines from 3.0L to 8.2L, covering Volvo Penta SX models from 1994–2006 and OMC Cobra SX models from 1994–1998.
It serves as a direct interchange for Volvo Penta part numbers 3855275 and 0778351, as well as aftermarket equivalents including Sierra 18-2598 and GLM 87750.
- Engineered as a direct-fit replacement for specified models.
- Designed for single-propeller sterndrive configurations.
- The package contains a complete 7-piece set of seals and O-rings for the lower gearcase.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Volvo Penta | 3855275 |
| OMC | 0778351 |
| Sierra | 18-2598 |
| GLM | 87750 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Volvo Penta: This kit fits a wide variety of SX-series sterndrives and associated engine models manufactured between 1994 and 2006.
For OMC: This kit is compatible with Cobra SX sterndrives manufactured between 1994 and 1998.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Volvo Penta | SX | 3.0L (181 CID) | 4-Stroke | 1994–2006 | 3855275 | Inline 4-cylinder |
| Volvo Penta | SX-C, SX-C1, SX-C2 | Various | 4-Stroke | 1994–2006 | 3855275 | |
| Volvo Penta | SX-CT, SX-CT1, SX-CT2 | Various | 4-Stroke | 1994–2006 | 3855275 | |
| Volvo Penta | SX-M, SX-M1 | Various | 4-Stroke | 1994–2006 | 3855275 | |
| Volvo Penta | SX-MTD, SX-MTD3 | Various | 4-Stroke | 1994–2006 | 3855275 | |
| Volvo Penta | SX-RT1, SX-RT2 | Various | 4-Stroke | 1994–2006 | 3855275 | |
| OMC | Cobra SX | 3.0L (181 CID) | 4-Stroke | 1994–1998 | 0778351 | Inline 4-cylinder |
| OMC | Cobra SX | 4.3L (262 CID) | 4-Stroke | 1994–1998 | 0778351 | V6 |
| OMC | Cobra SX | 5.0L (305 CID) | 4-Stroke | 1994–1998 | 0778351 | V8 |
| OMC | Cobra SX | 5.7L (350 CID) | 4-Stroke | 1994–1998 | 0778351 | V8 |
| OMC | Cobra SX | 5.8L (351 CID) | 4-Stroke | 1994–1998 | 0778351 | V8 |
| OMC | Cobra SX | 7.4L (454 CID) | 4-Stroke | 1994–1998 | 0778351 | V8 |
| OMC | Cobra SX | 8.2L (502 CID) | 4-Stroke | 1994–1998 | 0778351 | V8 |
| Volvo Penta | 302CMBYC, 302CMBYM | 3.0L | 4-Stroke | 1994–2006 | 3855275 | Inline 4 |
| Volvo Penta | 302CMHUB, 302CMLKD | 3.0L | 4-Stroke | 1994–2006 | 3855275 | Inline 4 |
| Volvo Penta | 302CMNCA, 302CMNCS | 3.0L | 4-Stroke | 1994–2006 | 3855275 | Inline 4 |
| Volvo Penta | 302CPBYC, 302CPBYM | 3.0L | 4-Stroke | 1994–2006 | 3855275 | Inline 4 |
| Volvo Penta | 302CPHUB, 302CPLKD | 3.0L | 4-Stroke | 1994–2006 | 3855275 | Inline 4 |
| Volvo Penta | 432APNCA, 432BPBYC | 4.3L | 4-Stroke | 1994–2006 | 3855275 | V6 |
| Volvo Penta | 432BPLKD, 432BPNCS | 4.3L | 4-Stroke | 1994–2006 | 3855275 | V6 |
| Volvo Penta | 434APNCA, 434BPBYC | 4.3L | 4-Stroke | 1994–2006 | 3855275 | V6 |
| Volvo Penta | 43APHUB, 43FAPNCA | 4.3L | 4-Stroke | 1994–2006 | 3855275 | V6 |
| Volvo Penta | 502APHUB, 502APHUE | 5.0L | 4-Stroke | 1994–2006 | 3855275 | V8 |
| Volvo Penta | 572BPBYC, 572BPLKD | 5.7L | 4-Stroke | 1994–2006 | 3855275 | V8 |
| Volvo Penta | 584APHUB, 584APHUE | 5.8L | 4-Stroke | 1994–2006 | 3855275 | V8 |
| Volvo Penta | 744EPNCA, 744FPLKD | 7.4L | 4-Stroke | 1994–2006 | 3855275 | V8 |
| Volvo Penta | 82FCPBYC | 8.2L | 4-Stroke | 1994–2006 | 3855275 | V8 |
Technical Specs
- Product Type
- Lower Gear Case Seal Kit
- Installation
- Direct replacement
- Fuel Type
- Gasoline
- Housing Material
- Various (rubber, polymer)
- Package Contents
- 7-piece seal kit
- Application
- For single propeller outdrives
What’s in the Box
- 1 x Seal Water Supply Tube (3854595)
- 1 x Seal Water Supply Tube (3852315)
- 1 x O-Ring Oil Passage (3852595)
- 1 x O-Ring Support Housing (3852866)
- 1 x O-Ring (3852865)
- 1 x O-Ring (333572)
- 1 x Oil Seal (3858303/3863090)
Installation Notes
- Ensure the engine is off and disconnect the battery. Secure the sterndrive in a safe, supported position, either tilted or removed from the vessel.
- Drain the gearcase lubricant completely into an approved container by removing the upper and lower drain/fill screw plugs.
- Following the manufacturer's service manual for your specific model, disassemble the lower gearcase to access the seals.
- Carefully remove all old seals and O-rings, taking note of their orientation. Use an appropriate seal puller to avoid damaging the housing.
- Thoroughly clean all sealing surfaces, ensuring they are free of old adhesive, corrosion, and debris before installing the new parts.
- Lightly lubricate the new seals and O-rings with a suitable marine grease or oil to ensure smooth installation and proper seating.
- Install the new components from the kit using appropriately sized seal drivers to press them in evenly without damage.
- Reassemble the gearcase, torquing all fasteners to the manufacturer’s specified values in the correct sequence.
- Refill the gearcase with the recommended marine gear lubricant to the correct level as indicated in your owner's manual.
- It is highly recommended to perform a vacuum and pressure test on the sealed unit to ensure integrity before submerging the drive.
Troubleshooting & FAQ
How do I know if my gearcase seals are failing?
The most common sign of a failed seal is milky or cloudy gear lube, which indicates water has mixed with the oil. Other symptoms include visible oil leaking from the propeller shaft area or a persistent burned lubricant smell. A failed pressure test is a definitive sign of a leak.
Will this kit fit a dual-propeller drive like a Volvo Penta Duoprop?
No. This seal kit is specifically designed for single-propeller Volvo Penta SX and OMC Cobra SX sterndrives. It is not compatible with Duoprop, Bravo, or other dual-propeller systems, which require different seal types and quantities.
What is the recommended replacement interval for these seals?
There is no strict interval, but it is best practice to inspect your gear lube annually for water intrusion. We recommend replacing lower unit seals every 3-5 years as preventative maintenance, or any time the gearcase is disassembled for service.
Do I need special tools for this installation?
Yes, professional installation is recommended as the job typically requires a seal puller, seal installation drivers, a torque wrench, and a pressure tester to confirm the repair. Refer to your sterndrive's official service manual for a complete list of required tools.
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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