953c 2zn742ss loader arms go up slow

I've got 953c 2zn742 track loader and today all of a sudden the lift arm started going up very slowly today . Fluid was a little low, so filled it up and no change. Run it a little while longer and looked at the fluid again and seem to be a little bubbly at the top. Anybody no what's the problem? Relief valves , seals , orings in the tank?:Banghead

953c 2zn742ss loader arms go up slow