I'm trying to improve the performance of a tilt/trim on an 80 HP mariner (mid 1980's I think) It is moving up very slowly. I have replaced the battery connection terminals, cleaned up the connections on the motor/pump and it has improved slightly. I'm at the point where I think it may be a fluid level problem. What is the correct way to check/fill the fluid? the serial # I found is 6287812. Thank you.