Looks like some moisture has gotten in there. Were you riding in the rain? How long has it been like that? If it did get wet, did you try to dry it out with a hair dryer or some other way. Heat gun would be too hot IMO and probably end up melting something. If it is moisture, even if it eventually dries off you probably still need to figure out how the moisture is working its way in since I would presume these parts should be sealed air-tight.