This is the pesky oil /water seal that sits at the base of the water pump that wraps around the driveshaft and separates water in your water pump and your gear fluid. It's one of the possible simpler fixes when you find water contaminating your gear lube. 
 
Oil seals prevent lower unit lube from escaping and more importantly keep the pressurized water, and other substances in the water out of the gear case.
 
Fits all Mercury V6 high-performance lower units including CLE, Torquemaster,  Sportmaster, SSM #4, and #6, as well as all fishing lower units.

Part Number: 26-16977, 18-2013
 
Includes one (1) Water Pump Oil Seal. Your application may require two (2) for some repairs.
 
Contact Mike Hill at STVracer@yahoo.com