On Thu, 06 Sep 2007 11:44:02 -0700, Mike C
wrote:

My trim tabs stopped working. I checked the fluid level, and it was
non-existent. I added ATF and switched on the tabs. The fluid all went
into the water. I believe only from the starboard hydraulic piston. I
have insta-trim tabs. I take it I have to replace the piston. How do
I do this? Does the boat need to be out of the water (problem!)? Is
there anything else I can check? There is no leaking inside the
engine compartment by the pump and I checked the hose connector to the
piston and it seems fine.

There are really only two possibilities that I can think of:

The hose is ruptured outside the boat; or, the cylinder is leaking.

Either way you're probably going to need a haulout unless you can find
a mechanic that works underwater or a really good diver.