The cutoff valve on the bottom of my '46 Two Ton's underseat gas tank has started dripping. It looks like the cutoff valve may be welded into the tank, or it just may be that there is a crud buildup around it. Anyway, I am concerned about putting a wrench on it and forcing the issue. Anybody have any experience with changing out this valve? Also, I can't seem to find the valve listed in any of the usual parts supplier catalogs.