Tuning Can a cracked pressure guage leak?

As others have said, no, just a cracked/broken lens will not cause an air leak. Problem is, what broke your lens. A hit to the gauge that broke the lens could have damaged the little very high pressure gauge, or less likely but possible, could have loosened its seal.

No need to guess. Get a small cup with a little warm water on the bottom and add a few drops of dish detergent. Froth it up by whipping it with a few fingers in the bottom of the cup. Apply the thick froth to any suspected leaking areas with your fingers. The suds froth will bubble up unmistakably showing a leak when you find one. JFYI, much better/faster/surer way to leak check small leaks than spraying a soap mix on.

jmo
 
My gauge was cracked as well. No problem with air pressure, leaks etc. But the crack was the proverbial canary in the coalmine. Upon closer inspection turns out there was a fissure between the thread and the body of the gauge as well. That explained its frustrating inaccuracy. It had probably been overtightened. A 3.5 bucks replacement from Aliexpress later -- problem solved. Feel much better about this gun now, funny how annoying such a smal issue can be.

🐦