Tilt question/problem? 86 merc/mariner 90 i6

[njrextreme]

Im having a issue with my tilt unit. Its a 86 mariner tilt set up for a 90 inline 6cyl.. The tilt lifts up and down when under no load. It will get pushed down if its tilted up and i start to go in the water. If I put all my weight on the motor when on the trailor, I can push it down also and hear a air noise coming from the main cylinder not the pump. Do you think it just needs the top seal replaced on the hydro cylinder? I dont see any leaks and the unit is full.