I haven't noticed any rust on my 2 inserts, but I do oil the insert before I shoot, before each shot. I have a bottle of NOW brand (from GNC) Almond Oil that I use for alot of things, oiling the insert and lubing the injector are 2 of them. I would hit the insert with some fine Steel Wool and oil the entire insert, and roll with it. Maybe You could oil the interior of the molds, too...that may (or may not) help with the sweating.
I did notice my molds kind of condensated when I pulled them out last week, I opened them and let the temp equalize and the sweat went away. Not sure if oiling the molds would help any, just kind of brainstorming.