Changing to an LED is easily done with some soldering and tips from the local tech store. Make sure you get the right sized resistor so that you do not push too much current through the LED and burn it out.
This said from the comments, it is not clear if this is a day time or night time problem. If this happens during the day, then the swap of lights will not make a difference. The lights only come on when the running lights are on.
Someone with big bucks could get the Autometers with liquid filled dials, I would guess this is the only 100% solution (a sealed face that will not fog up). This would eliminate the problem. But I live in Nevada. Never heard of humidity out here.
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