gauntlet foster fill fitting

[scion19801]

just found my fill adapter is leaking. anyone know what size o'rings go into them. this is on the hajimoto's (jsar adjustable) flex regulator fill fitting that has the check valve in it. wondering if i can just try to replace the o'rings and get it sealed back up, versus having to buy a whole new foster fitting. it is leaking from inside the check valve, not where is screws into the regulator.