I have been dismantling a few gauges and cleaning the lenses, amazing how much better and old shitty gauge can cone up.
The screw driver method works, ease the lip back a little at a time as you go around and went round about 3 times, less stretch in the lip. Your bike is the 75 so if you take your gauges out of the bracket the shock ring rubber between the gauge and bracket could well be heated on. these rubbers are unavailable as far as i know and i haven't heard of a replacement