Finally, last week, it gave up completely and stayed in bed.
Date of manufacture is May 2001 and it came as part of several Pentium class computers I bought second hand earlier this year on (you guessed it?) eBay! At the time of delivery and for some weeks subsequently I had no complaints about it at all, so I can't reasonably ask for a replacement.
I'm tempted to throw it in the trash, but if it's of use to someone for parts or repair, fine.
Warning: if you don't know what you're doing, don't be stupid. CD drives contain lasers. You can damage your eyes if you run the drives with the cover off and are ignorant of the precautions to take.
It weighs about 800gms, so together with packing materials I expect about 1 kilo, so postage is 3.67. I'm making no charge for packing. It will be well packed, using recycled packing materials.
I also have a Sony CD drive, model CDU701 (manufactured Aug 1998), which struggles to open its tray. If you want that instead or you're prepared to pay the extra postage, just let me know (3.56 extra). Or better still, buyer collects (location is about 5 miles from M25/J11, or similar distance from M3/J3).