Top tray very insecure - Zanussi DW908 dishwasher

Question

I have a problem whereby the top tray keeps coming off of its runners. Either the wheels fixed to the side of the dishwasher fall off or the tray pulls out of the runners. In either event the tray drops down. This is a very frequent occurrence. There seems to be a lot of loose play where the wheels push on to the fixings in the dishwasher side.

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