You don't replace it - it must be taken apart, cleaned and lubricated. It can all seize up in dry lubricants. New idler wheel, new lifting arm friction pad and a new belt. The motor will almost surely also need new bearings in order to run correctly. All of these parts are available. Martin

Hi Martin, thanks for the advice. May I ask for your help with two things please? Any idea where I can source the parts? Secondly is there a recommended lubricant? Many thanks, Richard.

I like to use a teflon-based oil called "Liquid bearing", but any good long-term oil or light grease would be fine. Parts here. Martin

That's really helpful - thank you! I had the motor replaced a couple of years ago so I think that should be fine but I have noticed the re-assembly of the parts was wrong with inversion of Spacers causing some impacts which I have now fixed. I don't have the service manual so may I ask for your assistance with one more question please?  Please see the attached image from Beoparts of the idler wheel underside. My question is should the end of the lifter arm fit into the slot in the side of the brass bush or does the brass bush sit on the idler arm held in place by gravity? In the slot appears to make more sense.   Many thanks,   Richard

The lifter arm with the small pad should work in the groove, so it can lift and lower the wheel. Martin