Handyguys, you know how I think.
I just wouldn't be satisfied if I replaced it all and still didn't know what the actual problem was. I'm an investigator. It's all in the details.
I'll try the baby powder trick. It just runs for about 10 seconds every 20 minutes or so. I can't hear any water drip or trickle, can't catch it in the act, and as I mentioned I cleaned around the flapper and such. Frankly, I'd like a whole new toilet because it's an old water hog (I've adjusted the tank level, but it's still wasteful), but that's REALLY beyond my ability.