>  the driver's side wiper works as it should, while the passenger side
> wiper moves spastically if at all, sometimes even crossing over into the
> path of the driver's side wiper.
>

Sounds like the splines on the passenger side wiper arm are stripped and
friction is all that's holding it. Sometimes the shaft friction is enough to
hold and it moves, and sometimes the friction is less and the shaft slips.
The wiper shafts run off the same motor via a linking arm, so they always
move exactly the same.

--
John Bange
'90 Vanagon - "Geldsauger"