Well I'm at my wits end. The toilet's been running for weeks and I've yet to catch it.
I first replaced the flapper, it still leaked. Then I replaced the flush assembly, it still leaks.
Now at this point I experimented a bit, and I filled the tank half way before turning off the water. It stayed steady for 2 days. But when allowed to fill properly, the tank completely empties over the course of 6 hours.
Could it be possible that the tank itself is somehow to blame? Could it be that I didn't tighten the tank down enough?