I'm assuming the gauge is on a regulator. About 40 years ago any part could be replaced including the diaphragm of a regulator, when I was learning welding only the out side parts were allowed to be replaced (you can probably guess where this is going) now I believe, no parts are repairable or replaceable (at least in industry in the UK) a damaged regulator is now scrap. They don't even do service exchange any more. Probably not a good idea to repair it.