Just replaced the headgasket and timing belt on my 1985 760T with 235K not because of headgasket problem but rather a cracked exhaust valve. Evidently because the valve was not adjusted in a timely way, it probably burned then cracked. Valves get thinner as time goes on and clearances get smaller or nil. I bought a good used head at a junkyard and cleaned it up well and installed it. The headgasket was okay, but I also wondered about it and finally decided to change the head, timing belt, belt bearing, meanwhile inspecting things. The pistons had a good amount of carbon that I picked off- it needed it- had a chance to examine the radiator, intercooler, harness and sensors and put on a used rebuilt A/C compressor that works great (learned to fill it with ester oil and charge the A/C system). All in all I would say that from 250k to 350k a head job with the trimmings is a good idea if you plan to keep her for another 100k or so. Somewhere I read that because of dissimilar metals in the block and head there is microscopic scrubbing of the headgasket due to different metal temperature gradients of expansion/contraction. I didn't see evidence of this. I think more damage is done by the almost inevitable blips of overheating when hoses, tubes, radiator or water pump get faulty or when the car runs wierdly with some problem. The redone head has given me good confidence in the old car once again. It feels strong and happy running on 4 cylinders again, and with a brand new headgasket and timing belt it feels all downhill! Psych! Good luck!