I have a 2000 bravo1. If I store the drive all the way up in a couple of days it will drop till the cylinders are completly compressed. Is there a check valve in the pump or are one or both of the trim cylinders leaking from one side to the other. Anyway to test?
A merc dealer can test the system with a pressure gauge set, They can find out witch cylinder it is or if its the pump bleeding off. In most cases its a cylinder leaking internally and thats a inexpensive fix. (hint) repair both cylinders at the same time....