Inspect your pulley again.
I am just remembering a case of a customer's 245 Diesel a year or two ago that came in with alternator failure to charge. I put a new Bosch reman unit on, with a new Conti belt, and sent it away. The car was back the next week... alt was fine but the belt was gone, completely missing. Checked out the alt pulley and discovered there was a bend in it, like someone had whacked the front flange of the pulley with a hammer. The pulley consequently had a narrower point in it, which was evidently pinching and stretching the belt once every 360 degrees of alternator rotation. The belt was destroyed in short order.
I still had her old core unit around so I swapped the pulley off of it, which was in fine shape... put on another new belt and the problem did not return.
You seem to have exhausted all the typical causes of this sort of problem on these cars.... now you get to start looking for the weird ones.
