Try this:
With the gas on
Take off the regulator knob/cap, and take out the brass piston, if there is leak noise from the place where is a litle pin sticking out, you have a busted o'ring on the other side of the regulator.
Time to replace.
Just turn over the gas, de-gas, the marker, and replace the damaged o'ring, you'll see what one is it after you open the remaining regulator, it's the one that goes in with the pin.
Hope this help.
Read the maxflow manual for more info.
Cheers
Jaime Menino