B7100 hydraulic issues

I have an early 80s b7100dt (gear driven) and I am having a couple of problems out of the Two hydraulic systems.

1) the 3 pt arms slowly lower while I am mowing. The problem seems to have been worse recently , I find I really need to raise and lower the cutter after every pass to make sure I get an even cut. The hydro oil has been changed and the filter cleaned but that didn't change anything.

2) tractor has a fel with a hydro pump driven by a shaft off the front of the motor. The fel works but lacks the strength it had a month ago, for example if I put the bucket on the ground more often than not it won't lift the front wheels off the ground. The fel hydro system uses one of the supports as an oil tank, I found the pickup line at the bottom of the tank has a screen which I cleaned. Oil level is fine . the weakness started after I used a rachet strap to pull the bottom edge of the bucket up so that I could weld a crack, not sure if this is a coinendence or what may have caused the problem

What are the possible causes of these issues and how should I go about troubleshooting them?

Ok so on the 3pt i'll need to get into the control valve and replace seals?

On the loader, it is still fully functional just not as strong. If I move the lever several times it will actually lift the front wheel but if I grab the lever and hold it open when the loader hits the ground I hear a hiss noise in the control valve which makes me think it has something to do with pressure relief, maybe as simple as an adjustment?