Pictures speak a thousand words
What exactly do you mean by the top rim being sheared in half? Just the plastic part?
Generally the plastic rims do very little structurally, the tank is actually held in place with just the silicone. I would bring it outside, place it on a piece of foam or cardboard, and fill it up. Best way I know to see if it leaks
And if you have a leak that's fixable too; scrape the old silicone, clean the glass really really well, and reapply silicone. If you have to do this I would suggest looking up a build your own glass aquarium thread and follow their directions on proper silicone technique.