I just finished cleaning up my roof drip rails. I cleared all of the filler out of them. I am not sure if this was correct, but they were flush from the lip to the edge of the roof with what looked like body filler. I am wondering if I need to put body filler back in there. I think I have seen some kind of epoxy or something that is used in the rain gutters to keep them waterproof. As it was, when I stripped the body filler out there was a little surface rust at the seam. This is a place that will always flex it looks like and if I put hard body filler in there it will get little cracks in it and hold water, which is what looks like happened with the earlier body filler. I would like to fill this in with something that will last and keep waterproof. What has everyone else done?