anyone have experience/knowledge of fuel cap specifics on 71 transporter?

situation is, present cap (unknown if correct cap or not) leaks.  looks like
it's vented-maybe.  filler neck looks like a type 1, type 1 cap fits but not
sure about venting situation.  also, I've checked 'Stant' locking gas cap
books and they skip right over 71 model year indicating none available (?).

anyway, thot I'd check here first for anyone who's been down this road
before.  Joel?  71 looks like a unique year for bus gas cap I guess.

thx/ken wiebe