Clean it off with some WD40.
Based on my experience, I'd say you just found root cause.Irelander said:"He carries his P380 in an Uncle Mikes pocket holster which I believe is foam lined. He probably keeps it in that holster all the time..."
i have an Uncle Mike's IWB holster for my P380. I have used that holster for over 1 1/2 years and for the most part store it that way inn my safe when i am not wearing it. I have never had a speck of rust.. occasionally i put some CLP on the slide but that is all..I think there might be some other problem than just a foam lined holster.