Is the Carollton a two piece toilet (can't remember)? If it is, instead of leaking past the flapper, it could be leaking past the gasket sealing the tank to the bowl. If so, then you may need to pull the tank, tighten the nut holding the flush valve in place, then reinstall. If when you run your finger over the flapper seal, if it is smooth, then that's not likely the problem.
Also, make sure that the flush handle and chain are adjusted properly - there shouldn't be too much slack in the chain, and it should pull up nearly straight, and not pull to the side. If the flapper wasn't stored properly, it could get warped or distorted. When looking at it, does the sealing surface appear to be flat or is it warped?