Sierra 18-2003 Oil Seal for MerCruiser Alpha One Upper Gear Housing, Replaces Mercury Marine 26-68493 26-823894

The Sierra 18-2003 is an upper gear housing oil seal built for MerCruiser stern drive applications, including the Alpha One, Alpha One SS, and Alpha One Gen II family of drives. It is designed to keep gear lube contained within the upper drive housing while sealing out water intrusion, protecting the gear set and bearings from contamination and premature wear. The seal is white in color with a rectangular profile and is a lightweight, single-piece component intended for straightforward replacement during upper gear housing service or seal kit rebuilds.

This seal cross-references directly to Mercury Marine OEM part numbers 26-68493 and 26-823894, making it a drop-in equivalent for owners who prefer an aftermarket-priced option without deviating from OEM fit and function. Fitment spans a wide range of MerCruiser drive applications and model years, from early 888/228/250/260 units through Alpha One Gen II (CR) drives. Because a gear housing seal is a wear item exposed to constant lubricant and water contact, replacing it whenever the upper housing is opened for service helps prevent leaks and gear lube contamination.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-2003
• Color: White
• Shape: Rectangular
• Weight: 0.06 pounds
• Country of Origin: Taiwan
• Package Quantity: 1 seal
• OEM Cross Reference: Mercury Marine 26-68493, 26-823894

Fitment

• MerCruiser 888 / 228 / 250 / 260, 1977-1982
• MerCruiser R, 1983 & up
• MerCruiser MR Alpha One, 1984-1990
• MerCruiser MR Alpha One (CR), 1984-1990
• MerCruiser Alpha One SS, 1986-1989
• MerCruiser Alpha One Gen II, 1991-1995
• MerCruiser Alpha One Gen II (CR), 1991-1995
• MerCruiser Alpha One Gen II, 1996-1997
• MerCruiser Alpha One Gen II (CR), 1996-2010

Replaces (OEM)

• Mercury Marine 26-68493
• Mercury Marine 26-823894

Frequently Asked Questions

What MerCruiser drives does the Sierra 18-2003 oil seal fit? The Sierra 18-2003 fits MerCruiser 888/228/250/260 drives (1977-1982), MerCruiser R (1983 & up), MR Alpha One and MR Alpha One (CR) drives (1984-1990), Alpha One SS drives (1986-1989), and Alpha One Gen II and Alpha One Gen II (CR) drives (1991-1995, 1996-1997, and 1996-2010).

Is the Sierra 18-2003 the same as a Mercury Marine seal? Yes, the Sierra 18-2003 cross-references directly to Mercury Marine OEM oil seals 26-68493 and 26-823894, so it fits and functions the same as the genuine Mercury Marine part.

What color and shape is the 18-2003 seal? It is a white, rectangular-shaped seal designed for the upper gear housing of the specified MerCruiser drives.

How much does the Sierra 18-2003 oil seal weigh? This oil seal weighs 0.06 pounds.

Where is the Sierra 18-2003 oil seal manufactured? The Sierra 18-2003 upper gear housing oil seal is manufactured in Taiwan.

Is the Sierra 18-2003 a genuine Mercury Marine part or an aftermarket replacement? It is an aftermarket Sierra-brand oil seal, not a genuine Mercury Marine part, but it cross-references to Mercury Marine 26-68493 and 26-823894 for equivalent fit.

Does the 18-2003 seal fit the Alpha One Gen II (CR) drive? Yes, the 18-2003 fits Alpha One Gen II (CR) drives for the 1991-1995 and 1996-2010 model years.

How many seals come in a package? The Sierra 18-2003 is packaged as a single oil seal per unit.

Does the 18-2003 fit the early MerCruiser 888/228/250/260 drives? Yes, this seal fits MerCruiser 888/228/250/260 drives from the 1977-1982 model years.

What is the OEM cross-reference number for the Sierra 18-2003? The Sierra 18-2003 cross-references to Mercury Marine 26-68493 and 26-823894.

Will the 18-2003 fit an Alpha One SS drive? Yes, the Sierra 18-2003 is listed for MerCruiser Alpha One SS drives from the 1986-1989 model years.

What is the 18-2003 seal used for? The 18-2003 is an upper gear housing oil seal used to retain gear lubricant and keep water out of the upper drive housing on the listed MerCruiser applications.