Hi Ron.  Glad you found a suitable vehicle :)  I don't use synthetic 
(never have), but I do use Castrol GTX 20w-50 (10w-30 winter) in our 
diesel Golf and our van.  I've been using this oil for years, and 
have had excellent luck with Castrol products.  Frequent oil/filter 
changes are the key.. I do every 3 months/6000 km (3600 miles) 
whichever comes first.  Keeps the engine clean that way.

>      1) Is synthetic oil good to use in a 1990 Vanagon?  (Mobil 1 or equiv.)
>         I've always used it in my 1987 golf, and I think it's one reason the
>         engine is in fantastic shape.

I use Chevron Supreme 92 octane in our van.  Chevron fuel is 
excellent and the additives they put in the fuel (techlorine ?) 
really does work well.  Keeps plug deposits down to a minimum.  It's 
my first choice fuel.  The van apparently will run on lower octane, 
but I've always put in 92 Supreme.  It starts right away, and never 
any power delivery problems.  This fuel is also excellent at keeping 
the injectors clean.... an important concideration.

>      2) How about fuel?  I've always fed my Golf the highest octane available,
>         but I've been told that this is essentially a waste.  Opinions?
> 

Congrats

Harry. 
------------------------------------------------------
Harry Yates      Internet: hyates@bcit.bc.ca  Burnaby, BC
'90 Syncro Westfalia
'87 Golf Diesel