There is an EGR passage that goes
through the head and into the intake
manifold, I don't know what a Welch
plug is, sounds like a muffler bearing,
you might not what to use that guy
for your repairs, for a fix, try to tighten
the intake nuts/bolts in the back where
the EGR comes through, and Plagued

I don't think I've ever heard of this problem
Wild