The owners manual only talks about ajusting the fan height to tighten the belt. The belt seems well past that, so needs replacing. I suspect it was considered one of those jobs every body new how to do at the time, so they didn't consider it worth mentioning. The belt looks as though it may able to be split and re-attached. I don't want to try this until I am sure, and have a suitable replacement. The car is at least drivable at the moment - if noisey.