Is 5 k hours a worn out machine?
That's a tough question to answer. Some people consider a 5000 hour tractor to be worn out, while others do not.
Personally, I think 5000 hours is approaching the time when major work such as an engine overhaul will be required, so I generally like to see 3000 hours or less, preferably the latter. Regardless of how many hours the machine has, assuming the hours are even accurate, condition is everything. If the machine was well cared for it could have a lot of useful life left in it, but if the machine was worked hard or abused it could need major work.
Look at the pedals, 3 point linkages, and drawbar for signs of excessive wear, indicating a lot of use or abuse. Does the engine have any unusual leaks, sounds, or vibrations? Does the transmission shift gears smoothly? Look at the bottom of the transmission bellhousing for a hole with a cotter pin sticking out of it, then give the cotter pin a spin to make sure the hole is open. Does it leak excessive oil? Some minor leakage is usually normal, but a steady drip indicates problems with either the engine or transmission seals. Are the tires and rims (especially the rears) in good shape? Rear tires and rims can be expensive to replace. Evaluate the clutch and brakes for slippage by applying the brakes and slowly releasing the clutch to see if the engine tries to stall or if the tractor starts to move.
Carefully evaluate it's condition and factor in costs (and work) associated with making it a good working tractor, then make your offer accordingly.
The following is a link to an old TBN thread which might be helpful about a tractors lifespan.
http://www.tractorbynet.com/forums/buying-pricing-comparisons/10459-tractor-life-span.html
