I am at a loss of what to do with this one. I recently purchased a house built in the 1950s. In the second bath, there's a Sedona toilet that has been leaking. Upon further inspection, I found it's a tank-to-bowl rubber washer that wasn't sealing all the way. The toilet was also running periodically, so I bought a Fluidmaster repair kit and replaced everything, including the tank-to-bowl hardware. However, the leak persisted. It is only a leak from the left bolt, closest to the water supply line.
I've tried replacing all of the rubber washers a second time, and even bought thicker beveled rubber washers but to no avail. I do not see any hairline cracks/chips in the porcelain and scrubbed the area under the washers as best I could.
I don't really want to silicone under the washer, as that seems like a "cutting corners" method - it would be annoying to remove if it didn't fix the problem, too.
Any advice for me? Here's a picture