Mercury trim rebuild
 

I have an 2002 75HP MERCURY. water got into the cylinder over the winter 2 years ago and split it. I bought kit #8M0055015 and kit # 89302A01...Not a complete rebuild kit. I put it back together. it worked for a time, then lost pressure. I burped it. it was working again, but by the end of the season it had lost pressure again. There is a small metal piston, about a 1/2' in diameter with 3 O rings on it. The piston is pitted. As I look at the diagram, Kit #5... 8M0090404, it indicates that the small metal piston is part of that kit. Can anyone out there corroborate?