I'm looking at buying this diesel Ford 3600 tractor. Seller says recently he noticed while mowing tall grass with 5 foot brushhog, the PTO was barely turning. This tractor has a live PTO. When letting out clutch, first the PTO turns, then when pedal is further released tractor starts to roll. Tractor drives fine in all gears, only the PTO slips while under load. No clutch is installed on 3 point driveshaft. Tractor has around 2500 hours. Before I buy this I want to know if I can tell whether it is just an adjustment or if clutch needs to be replaced.