Sealed unit with an LED inside.
Would be worth taking out and bench testing to make sure it's broke.
If so, you could try and get crafty and fix it, but probably better to just get a new one.
Edit:
Just took a walk around the car and guess what! I have one out, too.
So I guess we'll figure this out together.
I don't have a bulb warning though, so I think you have something else going on. I didn't think those were monitored.
My left rear marker has the tiniest little glow. It flickers if I tap on it, but it won't stay lit.
It probably has a surface mount LED that's now a surface dismount.
Friday I'll make sure it's not just a connector issue, then pop it out and see what's what.
If I think I can get it apart without cutting myself I might just do that.
I can probably resolder it, but probably not reseal it, but it will do while I order a new set.
I wonder if any forumites have done a delete and have theirs just lying around?