+1 on Timeserts, given 2 helicoils failed on my mower I wouldn't be too keen on using them on a car engine. I would imagine by the time you removed and stripped the engine, paid for a pro to do the Timeserts, inspect & machine the head, new fasteners and gaskets etc etc it would be more cost effective to just pay the $1500 - odd and throw a replacement engine in the hole. Disadvantages to doing that too, but damned if you do / don't really!