Well this is embarrasing! I just pulled my engine to put on the heads that sat in storage in L.A. for 5 years... and found that whoever last put my exhaust back together (me...), didn't tighten the hanger nuts.

Here is the result:
Click to view attachment

I guess it was loose and just wore into the studs. What do the holes of the bracket look like?

Looks like your going to have to drill the studs out and replace them. Be careful.