It turns out that the (likely) answer was already posted in the
archives, although I did not find it when I searched before posting.
Thanks to Mike Collum for pointing this out to me, and to Paul Guzyk for
his excellent, definitive pictorial reference on the topic.

http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind0408e&L=vanagon&D=0&P=7453

Jim Kurpius wrote:
> The same thing happens on my 84 westy...I don't notice that setting it
> makes any difference...if you find the cause please post and pmail me.
>
> Thanks, Jim
> 84 westy
> SF Ca