I know this has been beaten to bits, but they changed the neck so the caps from Geno’s won’t work. This is my temporary fix. A 2” ABS cap covers it so at least if DEF is spilled, it won’t go into fuel tank. I’ll be calling Geno,s but there are ribs now in the neck, so it won’t seal. If you look closely at the neck in the background you’ll see the blue cap not sealing from the rib, there are three ribs to prevent o ring from sealing.