[Vwdiesel] Dead alternator tensioner on 85' Golf diesel

[Pam & Doug Boes]

   My daughter came home this afternoon complaining of the alt. light 
being on and the engine making a "funny noise". When I opened the hood, 
I could see the tensioner pully for the alternator belt had all but 
disintegrated. The pulley was still there because a large washerlike 
piece kept it from falling off. However, it had no gap on one side and 
about a 1/2" gap on the other around the bolt. It doesn't look like 
anything is salvageable except maybe the bushing that goes over the 
bolt. If I call an auto parts store to order a new one, what is it 
called besides "alternator belt tensioner pulley assembly" that would 
describe what I am looking for? Same question for if I have to order 
from the stealership. Will they know what I'm asking for?
I've never seen a failure like this one before on a VW. It looks like 
the sheave portion of the pulley separated from the hub portion so that 
the sheave has about an 1 1/2" hole and no way to center it on the bolt.