There are many other products for that rusted area and they aren't JB weld. One of the first things to think about when cleaning up a window channel is how smooth does it need to be? NOT very smooth that for sure. If the entire window channel is pitted rust but still structurally solid why smooth it out? The window sets on a bed of urethane, the metal under that urethane can be pretty darn rough, it isn't going to matter one bit if it is pitted metal cleaned properly and epoxy primed. AS LONG as it's cleaned properly and epoxy primed it doesn't need to be smooth.