I remember this thread...Hehe, lots-o-fun.
I think my best one by far has to be replacing my head gasket three times.
First time, head warped.
Second time, the head I used, a PO put shorter valves in that wiped out my cam.
Third time, Realized after blowing number 5 seal that the head is an N42 on an F54 N/A block. Compression ratio that would require more work...