>I've installed new seals. I've narrowed it down to the O2 sensor.  Since it
>has never been installed on the Vanagon.

Hmmm,  you mean this sensor works telepathically? Wow, cool.  I ran my '85
without a sensor for several years, runs rich and does affect the mileage.
No hiccups though, the brain has a default value for when no signal is being
received. Always started etc. It did however like to backfire if you gave
even a tiny bit of throttle on a downhill/coasting run.

  I suspect the custom exhaust system fabricated from a set of bug J-tubes,
copper and cast iron plumbing fixtures, several sizes/shapes of muffler
tubing, some flexi-pipe and vestigal remains of the stock system played a
part in this. Not to mention the generic $29.95 Toyota muffler, "yeah, about
that big, maybe a bit longer and say 4 or 5 inches across, give or take a
bit"  FLAPS guy found the perfect match in less than 2 minutes :>. Needless
to say the O2 sensor was an optional extra for this system.

Tim Smith