I have used these valves on many airplanes, and the only one I had fail was the GP brand while still very new. After that I started using the DuBro exclusively and haven't had any problems. I'm sure the GP is as good as the DuBro and I just got a lemon, and in a pinch I'd buy a GP again if I had to.

As suggested by rajul, all will eventually leak, due to wear on the o-rings. The way I look at it, the fueler valve is an expendable convenience, and *should* keep an extra one in my flight box.

Fuel dots are often difficult on cowled installations like your P-51 unless you have two vent lines to the tank or a carb with positive fuel shut off. If you don't mind spending another $12 for a new fuel valve, it is probably the easiest way to go.

One thing I do is give my valves an occasional oiling with light machine oil or after run oil to keep the o-ring slick.

Dave