Damper-Dampner, whatever is probably shifted the rubber could ahve ripped or slipped, either way it's hard to check, but #1 symptom is wierd timing pointer position. Same thing on my F150, every time I turned on the car and reved it a bit the timing pointer was in a different place, then it stuck at about 45 degrees off. I had to time it by ear, and surprisingly when I had to smog it, it ws right on. Go figure.
Simply marking the pulley might not solve it 100%, it could move again. If your belt was off a tooth, it would be only about 3-5 degrees, and if the belt was off 20+ degrees, it would not run.
Try that, and hope I helped.