The good new is, a quick and simple visual inspection is all that's needed to avoid this problem. If any cracking around the outer part of the pulley is evident ( the rubber section at the circumference ) replace it. I've seen several that have deteriorated so badly that there's a noticable wobble of the pulley that can be seen with the engine at idle. Unfortunately, the first failures resulted in front cover replacement,etc. We'll all be doing our clients a favor if we replace the marginallly worn pulleys before it's too late.