This is a commin problem on USa built vehicles in the 80's.
Problem is the rims flex, a tinny bit causing the wheel cover to move.
I've never seen this on the Vanagon.  Check and make sure the wife
is not rubbing   up against curbs.  Also check to make sure your
lug nuts are tight.

                                                     Eric

Jim Morgan wrote:

>Hello all.
>A new craziness has appeared on the van. It seems that the stock gray plastic
>wheel
>cover has rotated its self and cut the valve stem producing a very slow leak.
>Has been driving me crazy putting in air and using soapy water to locate it.
>Minor PITA.Has any one else experienced this? Well, add this to the list of
>things to check.
>
>       : )  JIM
>
>
>Jim Morgan 86GL
>"Breadbox" 208,000.0
>Westlake,Ohio
>
>
>
>