It has been 9 months since I first posted about my holding tank leak, but I wanted to report the outcome of the problem in case anyone else discovers the same trouble with their system.
Tightening the flange nuts did nothing to resolve the problem, so I removed the toilet, flange seal and flange ring, inspected for cracks or other obvious problems within the drain pipe (found nothing), cleaned the threads at the top of the drain pipe and applied pipe thread sealant, then re-installed the flange ring, flange seal and toilet. Upon flood testing the system again, I found that the problem had not been resolved.
I decided to contact my dealer's service department to see if they had any other ideas. I was told that there was nothing more that I could check without actually lowering or completely removing the holding tank, so I decided to let them take over at that point. After lowering the holding tank, the service tech found that the tank seal (which seals between the top of the holding tank and the bottom of the drain pipe below the toilet) had a split in it, thus preventing a watertight connection. They replaced the seal and repeated the flood test allowing the water to remain for 24 hours. Problem solved!
2013 Sunseeker 2300