The mystery is found. About 10 days ago Roger noticed water on the floor behind the sheetrock (water that would be hard to see once the floors and baseboards are finished.) Directly under the master bathroom where he had replaced a bent flange months ago. He took the toilet up and there was another bent flange, surely the reason for the leak. I found a new taller toilet for him to install. Installed. Leak still there. Each time until the 6th install he found something that might explain a leak...might should be in very small letters. (Months ago when he fixed the toilet the first time he said, 'there is no hurry to get a new toilet since replacing the toilet is so quick and easy.)
Last night after testing the drain pipe with a hose (with a spray nozzle) lowered and brought up 5 inches at a time he determined the leak was 5 feet down from the toilet. He cut off the newly textured, and painted sheet-rock and looked at the pipe. Two holes that look like they were made by a screw.... but no corresponding holes in the sheet-rock were found.
Now he gets to install the toilet for the 7th time.
edited Saturday evening; The holes are fixed, the wall fixed AND the toilet installed and working. Monday the painter will repaint the area.