Check the linkage as per Flushers page from the manual, the lever #6 where it clamps onto #5 & #9 will sometimes loose its grip and just needs the bolt tightening up. There is also a filter in the back which can accessed via the left hand side cover where the PTO engagement lever is situated. On this tractor it should be a square type filter held in with two 1/4" bolts (If my memeory is correct). It isn't the easiest thisng to get out through the side cover, but it can be done. Otherwise it is remove the lift cover and then access it from the top. Depends on access to lifting equipment? These are the two simple things that you need to check first. After that, then more in depth testing will be required.
FWJ wiil correct me if I have it wrong, but best of luck with it.