When running a/c water drips the drain plug at the passenger firewall. It seems to be quite a bit sometimes, I have seen the thread on replacing the foam gasket for the drip at the interior but this is more of a concern for the exterior. The water is dripping on this metal line which I think is for rear a/c. I want to do some preventative maintenance on this line. Should I just spray it with a rust oleoum spray can? File off some of the corrosion first? Any tips-this is the only rusted piece on the vehicle and it looks like the excessive drip over the years has caused it.