I've airbrushed many different AC lures and there's always two places where the paints Allan uses and mine react. The eyes and at the rear of the lure on the top half for about 1/2". I noticed you wrote plastic insert. Did you paint some of the Arbogast AC Plugs? Those are the only ones I know of that had a plastic piece in there. In any event putting a little epoxy in there should not hurt. Personally, I try to keep the epoxy out of there so it's easier to put the tails in. What tails did you put the lures? About a year ago I got some replacement tails from Allan, the Big Hammer tails also work well if your lure is larger enough. Good luck.