Up grading the sump isn't a bad idea, but it's going to take some time and some installation work. Even if you bought an off the shelf sump, there is still the plumbing changes needed to install it.
I'd order the new sump, but at the same time, repair the existing one. Yes, this means tearing the whole filtration system down, because your going to need to reseal the existing section, and this is going to need to be completely clean and dry before you start the reseal job.
I had something similar happen to me a couple of years back. I ordered an off the shelf sump, and installed that. This turned out to be a much more massive project than I though it would be. I found a lot of other things, like my skimmer, heater, ATO, that had problems, and needed replacement. It's amazing what you find when you tear something down. It's like a "This Old House" project. You got it apart, so you "might as well" correct anything else you find. The good part was now I have almost a new filtration system, using all DC controllable pumps, and all the cool stuff. The downside was the hit my bank account took.