Hold off on the comments on the subject.
  My 84 5sp with an ABA Jetta inline 94:. It's always seemed to put out a
little too much exhaust during backing up.  I've had "used-up",tired motors
in the past...smell like blow-by or burning oil.... the Vanagon I have now
smells like that, but ONLY when I back up....no smoking and no oil residue
on the back... Only when I got in reverse.
  I use a quart of 10-40 about every 1000mi.  Oil consumption hasn't
increased in about 4 yrs...
 Guesses, anyone?