[jagizzi]

I am going to suggest both Dicor self leveling and 4200, each in its place. I use both and each is a great product with many uses. Apply 4200 on the flange of the vent fan before sticking it to the roof. This creates a seal between the roof and the fan. The Dicor then goes over the seam on the vent and will level out over the seam, screws, bumps and gaps. The two together make a great, long lasting, weather proof, seal that looks neat.