just a suggestion.. sometimes if you know what you are doing with tools, repair is easy than a phone call.. if you actually can reach someone.. but I also realize that it also safer for some people who don't know what they are doing to leave tools in the box.. that said it's up to you to decide.. but I would guess the 3 screws on top likely remove the chrome ring.. and if it is made like I am guessing, either the glass will come off with the chrome ring or it's clipped on to the gauge housing.. you have to make sure you mark everything and keep it clocked right and definitely make sure when you reassemble it the pressure cutoff needle is on the right side of the pressure needle..
hopefully it helps but I totally understand if it is not something you want to try.. myself I fix everything unless under warranty, but then again I did a $1000+ repair on my John Deere while it was still under warranty.. because it would have cost me half a day each way to the dealership and then I really had to bail hay, not leave it to dry and burn out all the value ..
I just like seeing things work for people.. hate to see people get in over their heads..
Mark