Antony,

Call your local chapter of AAA (Auto Club). they provide a very inexpensive
and generally unbiased diagnostic service.

Most Vanagon odometers break when people inadvertently reset the trip
odometer while the van is in motion. Chances are, the van you're looking at
has had it's odometer replaced and/or repaired sometime during it's life.
Most unscrupulous seller's won't necessarily disclose that to you. Obviously,
you've already found that out.

Don't allow a friendly smile & claims of being a "mechanic" fool you into a
false sense of security. Have the vehicle professionally checked-out by
someone who has your best interest in mind. Although mileage can be a good
indicator of vehicle condition, it is rarely foolproof. There is simply no
substitute for a thorough physical evaluation. Buy based on the "effective"
age of the vehicle and not the perceived one.

A poorly maintained car w/ low mileage will almost always be inferior to a
well maintained vehicle with higher mileage.

BenT
San Francisco