[kiwi_steve]

Can you replace the drive belt (string) with an o-ring?  There has been tips lately that one can use a garter spring in place of a belt or o-ring.  Garter springs should last virtually forever.

I don't think so - I can't easily get a closed-loop in place without serious disassembly.  I have some wide flat hair-bands that I'm going to try super-gluing to a suitable length... failing that I'll await the day I need to replace the current setup...