I have a 68/3k Flatline and everytime I fill it up all the air leaks out slowly through the fitting on the reg.With the tank off.

The tank worked fine up to about a little over month ago,I shot about 30-40 balls and I got no pressure behind the trigger,I then noticed air was leaking out of the reg but the ouput gauge still showed about 850psi which would slowly go back and forth from about 650-950 psi.After about four hours the the tank went from 2800psi to about 200psi.After the output pressure got low enough for me to pull the quick disconnect there was no noticble air coming from the QD but still continued to leak out of the reg (this is with the tank off).

I took it to my local pro shop and they gassed it up and it didn't leak,so I shot about 100 balls and it starts leaking again.So I took it back to the pro shop and they cannot figure out whats wrong with it,It's been about 5-6 weeks since I took it to the pro shop.

If anyone has a idea whats wrong,please let me know it would be greatly appreciated.Thanks