Tractor Repair: Ford 2000 (Gas), bush hog, grass cutter

Question
My father-in-law has a Ford 2000 with a gas engine.  I work on small engines, not farm tractors.  His problem, the bush hog he has hooked up was working fine at a regular RPM but one day the RPM's just started slowing down, it even slows down with a grass cutter hooked up.  He checked with local tractor repair shops.  They stated you need to change the hydraulic filter.  This tractor is a late 60's model.  Does it have a hydraulic filter and if so where could I find it, or, do you think the problem is something else?  Thanks for your time...

Answer
Hello,

  It sounds like the pto clutch is slipping and will need to be repaired.  I have no info on a filter, but if there is one, it may be internal.  There are 2 different types of the 2000, a 4 cylinder and a 3 cylinder, and they are completely different tractors with different hydraulic systems.