I'm almost ready to open up the dash to replace the stereo, when I'm there I'll pop the dash panel out and see what's there. I've got a good stock of wedge LED's to see if they'll work if the panel has a removable base or not. try one at random and see what happens.They probably don't list them because either they are not dimmable with that setup or more likely its because the locking base is soldered to the bulb. This would make the bulb and socket one unit.
Below is a bulb and socket base unit. I believe you can buy just those bases without the bulb that allows you to remove the bulb from the base which would allow you to use LED bulbs.
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