I had already cleaned up all the rust I could reach from the top when I had the vent door off to replace the seal. I put on two coats of the stuff that turns rust black. The channel is only about 1/4 wide on the top, so I wouldn't be able to get a mirror in there. The only way I could see to seal it from the top would be to completely fill in that 1/4 channel. Didn't know if that would cause more harm than good.
