I had the same thing happen with a VW diesel pick-up with the same engine.
The breather fumes supply enough crankcase oil to the cylinders that it will
run on it, albeit fogging the highway at the same time.
There is a way to run a pipe from the breather on the valve cover so it tees
into the vacuum pump to crankcase return line thus allowing the oil to run
back to the crankcase.  This may help for a while.    Also, there is a
plastic baffle you can put over the camshaft inside the valve cover which
reduces the amount of oil getting to the breather.  This can help for a while
too.    In my experience though, at  high RPM it will still runaway
The only way to fix it is pull the engine down and put new rings in it.
I was able to do that, leaving the bores and pistons original therefore doing
the job cheaply.    I just pulled the head off, oil pan off and did the job
with the engine in the car.   Im not sure if there is good enough access in
the vanagon though.
Good luck
Steve Cotsford