Both of my AD trucks have (or had) this valve ('51 1/2 ton, and '50 COE) as well as my '42 1/2 ton. Unless you want to take a bath in gasoline, they are necessary to replace the fuel pump and are handy if you install an aftermarket fuel filter and want to change it. Fifty or sixty year old brass valves can leak once you start to open and shut them, so I have had to replace them. I too, have not seen genuine NOS valves for sale, but my local NAPA has no trouble finding an appropriate replacement with the correct fittings. I figure a leak free situation at the bottom of my fuel tank is not worth fretting over originality.
