I suspect that thermal contraction in the cooler weather is perhaps giving you the issue. You are wise to use any dielectric grease so it probably is not corrosion. I always use it on any car electrics when working on them. I really hate to revisit the same problem area again someday.

I would get a couple of the plugs off a wreck if you cannot retension the current contacts. Or creativly use aluminium foil with dielectric to tighen the connections in some form of creative way. Poor connections or less than optimum may continually degrade if high current is flowing as well.

The cycle till troublesome may just be circumstantial as well. The corrosion may have spread back up into an area of the connector where you cannot see it may also be another possibility. Especially in the area of the wire to prong junction. I might get it running temporarily and take my thermal gun to see if there is some form of abnormal elevated temperature when curent is flowing. In otherwords an unfound or unrepaired high resistance connection.