Managed to buy a new donut on eBay...doh I gave away the last one.

I wonder if it is worth making a 1mm thick steel ring for each side with a little play in the holes to tighten the donut up and stop it coming apart? Or maybe lock wire to limit movement?

I have worked out that the play in the centre bearing may have caused this and am fitting a new one plus making a better mount for it as I think mine was 2mm too high and putting the donut under pressure / vibration.