Can you change the bulbs in FL rear lights?
 

Just noticed - annoyingly - that part of one of the FL rear lights I had fitted has failed.

Offside boot lid light - the bulbs of the standard rear light aren't firing. Brake lights are fine.

Anyone know if there is a fix, and if so what it is?

Is it all the normally-on tail lights, or only a few out of the bunch? I.e. if, for example, 12 LEDs normally illuminate when you turn on the sidelights, is it all 12 LEDs, or fewer than that?

If it's all of them, it sounds like the light isn't receiving an input.

Any signs of water ingress?

I would take off and test it, maybe plug it into the cable for the other side.
If that still doesn't work I think you may struggle. The prefacelift you could take apart, but facelift seem to be sealed (from memory) with just bulb-holders for fog and reverse sticking out. Maybe I'm wrong but if not, I'd cut the back open with a hot knife and take out the PCB for repair and JB weld or low-modulus silicone sealer back together

Hmm. It's all of them.

Annoyingly when I got these (via German ebay - the last set then available) te outer lens had come off and partly been glued back on. I removed it and reglued it - so water ingress is the likely culprit. Might have to suck this one up.

Sale of goods act gives you 7 days from receipt. ebay gives you 14 days.
Even if your out of time, use ebay messaging to contact the seller. Send pictures to illustrate your issue, be super polite and ask for their help. They may be happy to help.

As far as I am aware SOGA is a UK thing and not applicable to purchases made elsewhere within the EU, such as these lights from Germany.

Unless it stated the problem ebay will deal with the dispute as a goods not as advertised.
Nothing to lose at all. Ebay is a law unto itself!