On the M117 it is usually a sign of intake gasket leak. Consider yourself lucky. Many times when the gasket leaks, those rear manifold bolts seize and snap. I had three snap on my 1985 M117. I got lucky and got them out by welding a nut on the stubs and soaking them with penetrant.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now