I had a broke pressure tap recently... the muffler got damaged on a wheels up landing.

Here's what I did:

First I closed up the damaged pressure tap hole with TechnoWeld.

Next: I was going to mount a new pressure tap with 3mm threads. But there's not much to tap in that muffler... it's pretty thin walled.

So I took a piece of 2mm piano wire and grinded a really sharp point on it.
Then I chucked the piece of wire in the drill, set the drill on highest speed, and pushed a new hole in the muffler wall...

This way the metal deformed inwards (be carefull, it gets hot), and I had more meat to tap threads...

I live in Europe, so I use metric stuff, but you could do the same with imperial threads...