Item: 71 bus fuel cap
Location: Bris but will pay post
Item Condition:must be in usable cond
Price and price conditions:you tell me
Other info: must fit the large filler tube, outside diameter is about 68mm and internal is about 58mm as a guide
Contact: Ian 04049874097 Bris 4012
cheers

I've got a '75 lockable fuel cap you can have (you pay postage) if that fits. It's OK, but I replaced it with a new stainless steel German one because I think it was allowing fuel to leak past on fast left-hand corners. I bought my new cap from VW-wagenwerks.com; looking at the paperwork it says "'74 - '79", so maybe it's different from your '71.

Try this page:
http://www.vw-wagenwerks.com/servlet/Categories 

hth