I "vented" my reproduction cap with a 1/8" drill bit through the plastic center on the inside of the cap. No more belch of fumes and no more giant sucking sound.
The new rubber (probably PVC) gaskets are real tight on the screws which prevents leaking.
I did the same. The new cap was not venting well enough so fuel was coming out where the sending unit mounts. No more raw fuel smell in the cab!
