The rear bolt has broken off on mine a couple times. I use a reverse
twist 1/8 drill and it usually spins right out before I finish drilling.
I switched to stainless bolts and use a full length gasket with my
headers and intake manifold, seemed to do the trick.
THis problem seems to be related to uneven torque on the bolts
I find the socket head bolts work a bit better casue I can torque
them in the tight places between the manifold and block better.
Dave