all the RFVC motors would run hot the 350 included, you just had to change the oil frequently. the fact that there are still 1984 and 85 XR350s and 500's still running around is a testimony to their reliability. 3rd gear was a problem on some bikes, but if the bike is still running it might not be a serious consideration. the valves and rocker arms and crank could wear fast if the bike was run low or on dirty oil. I would check the oil to see if it looked or smelled old or burnt. Other than that on a bike that old check for bent or cracked frames, loose suspension linkage or excessive engine noises, poor compression, general condition of bike...etc