Here's the problem. A small amount of clean water was oozing out from the bottom front edge of the caulk that seals the bowl to the floor tile. I could not find any visible cracks in the bowl. I decided to try using a bright orange dye. I dumped out the cleanser from one of those bottles that people hang inside their tanks. As the water level rises and falls in the tank some of the cleanser is released from the bottle. It's suppose to keep the bowl clean. (It doesn't work, of course!) I mixed the orange dye with water and filled the bottle. I told my friend to call me again after the toilet had been flushed a few dozen times. Maybe we could spot some of dye on the outside of the bowl if there was a hairline crack. We found nothing.
I pulled the toilet and flipped the bowl upsidedown. Again, the bottom of the bowl looked very good. The only thing left on the list that could cause a leak was the wax ring or the floor flange. Because I was in the home renovation business for several years, I've seen plumbers use every trick in the book to assure that a bowl mounted to an uneven floor will not leak. They use double or triple wax rings, or they take several pounds of plumber's putty and create a donut around the bowl horn. The idea is to seal the bowl so completely that it could never leak. I've seen these "tricks of the trade" fail too many times.
I thought I had died and gone to heaven when a company called Fernco developed a flexible rubber connector that always makes a leakproof connection between the bowl horn and the floor drain. All the problems of uneven bath- room floors, damaged flanges, etc., are irrelevant with this ingenuous flexible connector. For a 3" drain pipe you buy Fernco #FTS-3B. I've used it at least a dozen times with perfect results.
My friend's very fancy and costly toilet is still leaking. This problem is a real mystery! The water that oozes from the bottom of the bowl is never more than an ounce or two. It is not continuous. Weeks can pass with no leaking at all! Once the leaking starts it usually continues for several days. A plumber would have no patience with a problem of this sort. Naturally, he would suggest junking the toilet. I asked my friend to contact the factory and find out if he can get an exact replacement. His wife would be very angry if we installed a new toilet that did not match the rest of their master bathroom!
I hope someone can think of something I haven't tried.