I also have a cover with a crack in the same place. one is an inch long, and the other is 1/4 in long. both are from the vent tube and on the outside edge. the 1 in goes towards the rear and the 1/4 forward. they both start from the base of the tube.
can`t tell if the crack is on the inside since the vapor sheet metal piece is in the way.
I bought this cover from pick n pull & didn`t see it with the dirt on it. I have been in the process of polishing it, It`s going to look good.

I have a welder I use, I`ll see if he can weld it.
Charlie