Mine was missing on my 91 when i brought it.. ( didn't know it was supposed to be there). I had to get a replacement from E-Bay. The plastic post that broke inside was not repairable ( for me that is).
Thanks I have to take the bike to the shop will check if they can fix it or if need replacement. Worst case scenario will calculate gas milage with the odometer
Mine broke after a super glue repair. Pulled the gauge apart (time consuming!), removed the broken stub. Replacement made on dad's lathe, but waiting on the LH tap (3mm from memory). If you want more info LMK, otherwise buy one of the Morley speedhut gauges - I would have done it if $ permitted.