Right. Or, if you can't weld, use an M5 extractor/puller like this: https://www.manomano.it/catalogue/p...ere-estrattore-vite-prigioniera-m-6-3174233#/. I believe it is a M6 nut, but once you will collapse the thread it will be something about an M5 (if it is an M5, step down to a M4). I had this issue with a used head too.
^ this. Nothing else worked for me, would have been cheaper for me to buy a welder for this one job in the long run...don’t know how to weld though. to explain: i asked a local guy to come and weld nuts on to the studs. I still had one sheer but he is a good lad and drilled it out for me and helicoiled it.
I had this problem recently and used a mini blow torch inside the port to expand the area around the base of the stud. 5 minutes warming up and a pair of mole grips, job done.
