Well then you have the screw off type. yes that is different. If your valve is leaking Then you need to replace the whole valve pin assembly. The seat inside has been worn and allowing the gas to bypass. Or you can leave the tank on the reg and just back off the reg till no more air comes out. this will stop the leak , if your regulater is good. but it is a pain to do all the time. but it beats paying if you don't have to. The new on/off valves for those tanks should not be that expensive to replace. but I no everyone doesn't allways have cash. Try the backing off of the reg bit. This is all provided that you have checked the other areas for leaks. I have also seen the guages themselves leak inside the plastic. you may want to submurg the whole thing to check it . it all should be sealed. but only do it for a second. Or soap it up well to see bubbles. but it seems because you have the screw in type. it could also be the oring on the tanl leaking. Need to check and find out where the leak or leaks are. remember , if you find one, keep looking there may be more , until you check the whole assembly out.