Motor lowers slowly after trimmed up

[Triton owner 123]

I have a 115hp Mercury Optimax (Serial #1B703946) and noticed over the winter that the motor very slowly lowers to the ground after I trim it up a little. I would say it takes about 3-4 days to drop 2 inches. The motor raises up and down just fine and sounds strong so it is not the trim motor. I did some online research and think it might be the hydraulic pump or valve body assembly but I'm not sure. The part on the marine engine site for the Pump Assembly Kit is 8M0055019 and is $472, I could not find anything for the valve body assembly. But like I said not sure if that would fix it and is pretty steep $$$. The fluid checked out fine.

I'm looking for some feedback if replacing the Pump Assembly will fix the issue and if it is a difficult job. I'm fairly good doing moderate difficult work with some instructions (pictures/you tube). Thanks.

[Lowerider58]

Check the manual release screw and make sure it’s tight. If it’s not it can slowly leak down.