I have a 1979 40HP Mercury that I just changed the water pump. When I dropped the lower unit I found some rubber pieces. Some of the pieces had grooves in them that matched the spines on the drive shaft, and the part of the drive shaft that goes into the powerhead has no gasket. This is the first Mercury water pump I have ever changed. I have done a number of Johnson's and they all had a groove etched into the driveshaft that a O-ring sat in. My question is are the pieces I found what is left of a seal or gasket for the driveshaft, and if so what is is called? I have not had any luck finding anything in my manual and I have not found anything in the parts section of iboats.
