I got a replacement fan locally and fitted it. When removing the old fan, note well that the domed nut holding the blade onto the shaft has a LEFT-HAND thread!
Also, be aware that the insulation plate that fits between the motor and the oven casing will likely crumble to powder as you remove the old motor so you will probably want a replacement for that, too.
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this makes life easier for somebody! I've just finished the job and it took ages. Saved a bundle, though. New fan unit was £22 OTC (no delivery).MM