It would be helpful to know the make and model and year!
I assume the plenum is plastic, as I doubt you crushed an aluminum plenum.
If so you can probably build up the section with epoxy then when it hardens,
file it to shape and redrill the hole.
The outside corner of the bolt hole is compressed a bit, so the
surface of the plenum under the bolt head is not horizontal. The head
of the bolt will snug up against the plenum when I tighten it, but the
bolt is forced to lean to the outside.
It seems to hold tightly, but I hesitate to leave the bolt crooked
You might try dressing it square with a flat file and then using
a washer that's larger as described to spread the load.
Usually it's the one on the drivers side rear with the stud that
gives the most grief...
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