Slow Trim Leak?

[Ishmael]

I have a 2003 90 2 stroke TLRB and have been experiencing a small issue with my tilt and trim. In layman's terms, when I trim my engine all the way up, after a number of hours (overnight) my engine will have "fallen" down. There do not appear to be any leaks around the tilt and trim resevoir, and under normal operating conditions works just fine. Is this a seal issue? Any suggestions would be welcome. Thanks.

[boats.net]

An internal valve is not holding pressure, you might check o-ring on manual release valve, it's the only one you can replace without rebuilding power trim unit.