i have a Fountain 12 meter with SSMIII's and took the boat out last night and my starboard drive would not stay trimmed up when running, it would gradually drop and i would have to keep trimming it out. It stays in place when on the trailer and also when idle speed. No external ram leaks that i can see. Could it only leak when under power? Was late when i got back and wasn't able to check reservoir yet. Any advice on what to look for?

sounds like its possibly bleeding fluid past the ram seals when under a heavy load

Yeah, really the only thing it can be, figured if one of the seals were bad it would leak a little while stored but i suppose my only option is to pull em off and have them gone through.

Isn't there a check valve/ball at/in the pump or am I thinking of another application?

I am having the same problem with my Port SSM#3 fine on trailer' not leaking but wont stay trimmed under load.I believe there is a check valve/ball in the pump that is causing the problem I haven't had a chance to pull my pump apart yet for that side let me know if you resolve the issue i will do the same.

Will do, plan to run it this weekend so hopefully get it diagnosed. Let me know what you find if you beat me to it

If the pump is a prestolite pump (round motor on square plastic base) the problem is the control valve assy. p/n: 90762A2 bolted on the bottom of the pump with 4 bolts & 4 o-rings. The aluminum seat is not sealing the steel ball. This part is NLA from Mercury. This is a very common problem. The best solution is to replace the complete pump assy or a NEW control valve assy. Remember the TRS & SSM drives use a high pressure. The Alpha/Bravo pumps are not compatable. They don't have the pressure to trim under a load. The correct Mercury Oildyne pump p/n: 846859A4 and doesn't have this problem.