Roof Vent replacement questions

So I noticed our maxxaire II vent cover was missing a big chunk and one of the hold downs was broken off. I ordered another from etrailer, but when I got it, it is 2 inches narrower than the original. It would fit, but I would have to remove the old brackets which are screwed into the roof and install new brackets. The new instructions say to screw the brackets into the vertical vent flange (not the roof). There is a whole lot of caulk covering the brackets so I'm wondering what is underneath and if maybe the old brackets weren't installed correctly and someone just plastered it to protect against roof leaks. I'm about to go on a trip, so I think I may just do without the cover for now, and try to install the new brackets when I have time to recaulk. If anyone is familiar with what the vent surround should look like, I'd appreciate any feedback or advice. I'll attach a pic.

Edited by texastreehugger - Yesterday at 9:13pm