I came back to my boat the other day and the skeg of the lower unit was on the ground. I figured I just did something stupid and raised it. The next day, same thing. No external leaks I can see. I referred to my Merc Manual and it suggests 3 possible failures:

Poppet valves
Thermal relief valve
Trim cylinders

The manual says in order for the cylinders to be the cause both cylinders have to be bad, which suggest to me they are independant of each other. I'm gonna try to narrow it down to the pump/valve or the cylinders first. I figure the pressure guages are more than I wanna spend. So I'm gonna try to do this a low tech way. My initial thought was to test each cylinder by itself. Remove the oppososite cylinder, jack up the drive, remove the up/out hose and place a plug it the port. But that wont tell me anything because the problem could still be in the valves. How should I go about finding this issue?

i am having the same problem right now i am in the process now of testing everything i will keep you posted just going out on a limb here most every boby i talk too says they never seen the trim cylinders good bad the boat is 1996 so not that old