if you hear gas leaking past anything look at that part as being the problem.
the shutoff valve should not be causing any leaks at any other part other than to supply fuel to the converter/regulator and then on to the fuel mixer on the engine.
If you are hearing fuel coming from the mixer on the engine even with the key off then the fuel shutoff valve is stuck open (not completely closing) and should be replaced.
There is a neoprene seal on the valve inside that shutoff valve that deteriorates over time and can cause this issue. There is no way to effectively repair it, you just have to replace the shutoff valve. The mixer also has a diaphragm in it that should hold back the fuel when pressurized, if it is leaking past that then your converter/regulator may be bad causing over pressure to the mixer. You'll need to do a pressure test on the delivery side of that to verify the operating pressure which should be very low pressure, usually 2 to 7 psi. The converter should have the spec stamped on it, and there is a pressure test port plug usually so put your test guage at that test port.
If you want to be sure where all the leaks are coming from you can get a spray bottle and some soapy water mixture and spray down all the hoses, fittings, pretty much any part of that fuel system and if there is a leak somewhere it will show up with bubbles.