Get a professional engineer to survey both the aircraft/engine and its' technical (and modification) status...
I bought a 1979 build Warrior some 15 years ago and learned;
1. the factory corrosion treatment particularly internal is rubbish and patchy/non existant - look for corrosion and have the aircraft inhibited/treated properly
2. the wing bolts are almost invariably badly worn - 15 years ago £800 a set to replace
3. check the sealing on the fuel tanks
4. check the electrics and wiring looms
5. interior quality
6. check for installation, newness and warranties if any on the avionics - what I thought were decent (flashy) King Silver Crown kit turned out to be crap most of them failing within 2 years and probably not new when fitted anyway
this is basically a tin can with wings and frankly the build quality in my experience is not as good as many cars - at the end of the day you are looking at a 25-30 year old aircraft and there is inevitably deterioration so look for it
a new paint job and new interior can hide a multitude of faults - the smartest looking aircraft is not necessarily the best as technical quality and status is what counts
dont assume anyone selling an aircraft is anymore honest than a second car salesman and dont assume they necessarily know what they are talking about either