Try some silicone spray or paste, that softens and expands the rubber slightly, that may help.
To eliminate the moisture once it is inside the car, I use a thing called Hippo moisture remover, it's in a plastic box and absorbs all the moisture in the air.
They sell it in supermarkets to get rid of dampness in cupboards and under the sink, but it is the ducks nuts for keeping the car's interior dry.
About $6 and lasts for about 3 months. Moisture is the big enemy where electrical connections are concerned.
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