> cleaning the underside of the van last weekend I found some rubber plugs
> (in the rear, left and right hand side).

In the rear wheel well? On the outer edge?

Then you have a problem. On my �80 Red Cross T3 opening these plugs revealed
a water leakage in front of the luggage compartment.

In the van, next to the sliding door, just in front of the engine bay wall,
water was behind the side panels. I guess it came in through the window
sealings.
No need to say how rusty it was down there... I then sold that vanagon, my
first ever!

Raimund