yamaha 115 1991 trim problem

my 115 v4 runs well, but if I leave the tilt in full up position, the next day I find the engine full down . so I must stop it with the little lever every time .I don't see any leak of oil .
any suggest ?
ciao Stefano

[boats.net]

One of the internal valves are leaking pressure or the manual release valve not seating, it would have to be rebuilt to find bad valve or valve seat.

One of the internal valves are leaking pressure or the manual release valve not seating, it would have to be rebuilt to find bad valve or valve seat.

is it possible air in the circuit?
thanks Stefano

[boats.net]

If it trims up and down ok and fluid is full probably not air in system.