Great, Ill check out the page and try to figure it out. I found that this toilet is original to the house (circa 1945).
Thanks!
For what it's worth, sometimes the leak around the foam gasket doesn't come from underneath (i.e. the connection from gasket to bowl) but rather from above (i.e. the connection between the shank of the flush valve and the tank). I'm sorry that it took me so long to pick that up from your post and point it out. So, whenever you undo the tank to put in your next sponge gasket, make sure that you don't actually have a leak around the flush valve. Things to check include: is the gasket between the flush valve and inside of the tank making a good seal? Is the big nut on the flush valve shank under the tank sufficiently-tight? You don't want to overtighten because you can crack the china. What it should be is finger-tight plus 1/2 turn with a wrench or channel locks. If you have carefully tightened the tank down slowly, alternating one bolt then the next, a couple of turns at each bolt, holding the tank nice and vertical and making sure that your mounting hardware is pulling down vertical, stopping tightening the moment that you have any china-to-china contact, perceiving no wobble in the tank, there shouldn't be any leakage between the sponge gasket and the base/bowl.
It's amazing how some of these old units keep going and going, isn't it? Important historical perspective on quality American manufacturing of the time, even at wartime (which that was). Stuff was built well, installed properly, and, with some maintenance, could go 67 years!
We have one that is probably close to original, tank says 1926. Very-rarely-used. Not a very good flush. (It's a washdown flush that really doesn't wash everything down.) The Wolverine Brass ballcock and tank-ball flush valve will probably outlive me. The plumber installed them at some absurd price before I was paying attention to this stuff or understood it very well.
Then we have two left from the mid-1950s. Look great. Work great (particularly since I changed out the flush and fill valves for Korky ones). Not used much.
And one from the '70s, also still going. Less-sturdy, but looks good since I jazzed it up with a quality trip lever. Runs well since I changed out its innards with the Korky kit.
We replaced one bedroom toilet years ago with an early low-flow, which was so awful that we had no interest in replacing any others. When I finally started thinking about replacing the horrible low-flow, I found this site and lurked for a while. About a year later, I finally decided to go ahead with the replacement, chose Toto, and have been evangelizing its merits ever since. So we now have 3 Totos in the most-used places, all of which work splendidly and save water. I put them in right, so I have no doubt they'll probably be here as long as the house lasts.