replacing the guage is easy, it is help in but is very easy to remove, just use an adjustable wrench to remove the guage
***MAKE SURE THERE IS NO AIR IN THE TANK***
You can get replacement from planet (got one from them recently and works great)
Just put a bit of blue loctite on the thread so create a sealand screw it in with the wrench is very quick and easy to do
**leave the loctite to dry for minimum of 24 before filling the tank with HPA**
Hope this helps mate