I've got 4 Lee molds. Haven't had any problems with them yet.
I smoke the molds as the Lee manual suggests. I use a candle. The soot does not seem to last very long though.
I just read recently (can't remember where) that the purpose of the soot is not to lubricate the mold or act as a release agent. Instead, what I read said that the soot acts as an insulator to prevent the lead from cooling too rapidly on the mold walls, permitting better fill-out.
For what it's worth,