The lamps I've seen don't use a 1 watt LED, but 3 smaller ones.
MR16 are LV bulbs so nominally 12 volt. But a transformer would probably chuck out rather more than that if not fully loaded. And, of course, it is AC rather than DC. Test show the LED to be drawing the correct current and not getting too hot off 14V DC - the most it should see in the car. So hopefully a cheap and cheerful solution for a non critical application.
When I was at school, you could get the base off mains ones using vinegar. However, as the cement/glue contained some lead compound (to stop glass cracking with heat cycling), I rather imagine the H&S police will have found some other product nowadays, and that might no longer work.
Recently when I wanted some mains B22d caps, I saved up some dead CFLs, which were (mostly) easier to get the bases off than glass bulbs are.
Wish I could get the CFL that died today apart. It's only 7 years old and just has a loose connection somewhere - flick it and it flickers. Almost certainly easy to fix, but only if you can get it apart. I can get the tail-end off - the bit with the two contacts for the BC cap, but that doesn't pull far enough away to allow me to get anywhere. I can't split it at the center join - it just won't behave.
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