That's my thoughts as well.If it’s near the microwave it may be picking up the exhaust from the microwave.
Don't you need to use a specially formulated laquer to prevent corrosion or is that for when there is an issue with bi-metals? We have that sort of corrosion issue on the leading edge of the bonnet on our Jeep.Zinc die castings such as that display some awful corrosion occasionally, when you replace it spray the new one with a few coats of clear lacquer to give it a bit more corrosion resistance.