I have a 1996 40 HP mercury on a bass tracker. Tilt and trim have never worked quite right since I purchased the boat 2 years ago. The hydraulics never could keep the engine up, it always slowly sank (about 2-5 min). The first cold trip this winter, it got much worse and began to leak from the top seal of the piston. I could not find the seal kits so I did what I could do, drain the fluid and replace with new fluid. The old fluid was oil and it was frothy, I assume from water getting in. It took 4 or 5 times raising and lowering the engine with manual assistance to remove the old fluid. I used automatic transmission fluid to replace the old fluid. I found it impossible to use a funnel to add fluid due to the fact that the access hole faces downward when the boat is level. To solve this problem I lowered the front by cranking the hitch wheel as low as it would go and using a old gear lube pump (came with the gear lube container, it was very cheap) in the automatic transmission fluid container. I wrapped the end with Duct tape to increase diameter so that it would fit tightly in the access hole on the tilt and trim motor. I proceeded to pump fluid in till it squeezed around my duct tape, I replaced the plug and cycled all the way down and back up again manually assisting because it could not do it on its own. This I did 4 times before the Tilt and trim motor was able to carry the load by itself. I did this 4 more times until I could add no more fluid. At first the top seal around the piston continued to leak the new fluid then it stopped leaking on its own as the motor ran better. I don't know how or why this worked, but it works better than when I bought it. It no longer sinks at all, it is smooth all the way through from top to bottom, it is faster and sounds better. I was ready to give up and buy a new motor and pump.
