The "trick" (if there IS one) is to get the dried up seals to release. I've used all sorts of stuff but the best I've found is (and DON'T laugh!) PB Blaster. SMALL amount, preferably applied with a small paintbrush instead of just spraying it all ove everything. Let it "wick" into the seal all the way around the circumference of the bezel both at the glass edge and the "can" side. Keep the gauge "face down" and let it sit for a day, reapplying the Blaster periodically. One of the kitchen "jar lid" opening pads made of thin rubber helps grip the bezel too, when you try to turn it. Keep the "overage" to a minimum with that stuff... it MAY be nasty enuff to dissolve the paint, I've never let it get close enough to the dial faces to find out.
HTH!