Thought I'd have to fork out for a new DVD drive but it's pretty easy and quick to fix, as vid below shows. Managed to get an 'O' ring for next to nowt at the hardware shop outside Poros, a lot thicker and stronger than the original band in the DVD, which was no thicker than a rubber band so one of those would probably work if you can't easily get an 'O' ring. Could be that just a bit of a clean will do the trick - isopropyl alcohol (a.k.a. surgical spirit / rubbing alcohol) available from pharmacies.
Video is about 20 minutes long, could be shortened by about 17 minutes but saves a trek to the PC shop / waiting for delivery, as well as saving money.
Disconnect from PC / power supply before messing with it