Found a Mercedes OEM spec that says you can re-use their TTY headbolts as long as the bolt has not grown more then 2mm in length. So if a new bolt is 160mm and you pull and old bolt out of your Merceded head and it’s 161.5mm, you can re-use it. Interesting.
Am not advocating re-using TTY headbolts, and there’s no telling how much their bolts are like our bolts. But if a person was in a pinch and on the fence about re-use, this might help guide him separate “might work” from “really bad idea”.
Don’t apply this idea to rod bolts, that might be a whole different ballgame.