New Toto Drake Leaking

After reading about it on this site, we installed a Toto Drake 2 weeks ago after returning a Kohler Highline that didn't flush as advertised. We are very happy with the Toto's performance. 2 days ago it started leaking slowly where the left side bolt attaches the tank to the bowl. My husband tightened it a bit more, but it started leaking again the next day. He took the tank off, sanded around the hole top and bottom, still leaks. Took it off again, applied a teflon grease (Magiclube: a teflon based lubricant sealant) used for pool fittings around both rubber washers, and the black gasket for the trap, and it still leaks. This grease does not solidify. There is no metal washer between the rubber washers and the bolt heads as another reader asked in answer to a prior post. I tried to call the dealer and Toto this morning but they are not in on Saturdays. My husband noticed when he took the tank off that there was some water pooled up in the recessed area at the back of the bowl, where the tank sits. Any suggestions?

Since you have sanded the tank where the bolts drop through, the only place left if the flush valve.
That is the piece with the flapper.
Remove the nut from the bottom of the tank, pull the flush valve out and check for rough spots on the china. Sometimes a little sanding here will fix the problem. No goo should be needed.