Looking at the Bus Depot web site shows that the 251 201 139A was the
grommet for the 50mm filler tank used from 85-91 and probably for
California models 80 and after.  The 251 201 139 was generally for 80-84
models.  Bus Depot still shows the 139B model as being available but
doesn't list an application.

Their descriptions for Bus Depot's Gas Tank Sealing Kits 1 & 2 are my
source for thinking that the California models had the 50mm filler tank
on 80-84 Vanagons also.

Like Mark wrote, there are many other example of parts with a letter
after the number or different letters after identical numbers that will
not interchange.

Quite a number of them in fact are in this same 84 - 85 -86 model
transition period.  All 85's had some parts that were different from the
84's even though they retained the 1.9 and the Digijet FI system and
many other features of the 1st 4 years of Vanagon production, as some of
the new features that were destined for all 86 and later models were
introduced a year early.  85's made later in the year began to get some
parts bound for the 86+ models even though early 85's didn't get them.

Sam

Sam Walters

Baltimore, MD