p.t.o quit working on my mahindra max 28 xl hst , it started by slowing down then speeding up like something was slipping then quit turning altogether . i can feel it engage with the lever but will not turn and has no resistance when turned by hand . is there a clutch set up on the p.t.o drive and if there is can it be adjusted or are the clutch plates worn out . only 500 hrs on tractor. .