You sure it's not leaking past the drain?

If that's a possibility, I'd unscrew and reinstall the drain assembly per mfr instructions. (I can't recall if you're supposed to use plumber's putty or a bead of silicone under so-called "cultured marble".)

If the drain hole is the correct size ( on seconds, it often isn't straight or correct) and you installed your drain assembly with silicone, then the other option that may have caused the leak is that the drain assembly was overtightened, causing a crack. A cracked drain basically needs to be replaced. A crooked or incorrect drain size needs to be replaced. The only repair for such a top would be if the reason for the leak is that no sealer was used with the drain assembly. It would be foolish to pay someone to come out and loosen the drain assembly just to caulk it with silicone. It's a 5 minute DIY job. If that works, then your problems are solved. If not, then you've got bigger problems. The very act of cutting could possibly cause vibration fractures in it if done incorrectly, and while they may be willing to return it in original condition, it's doubtful they'll return it once modified.

I personally wouldn't throw good money after bad. I'd get rid of the seconds top and buy something else.