Okay, here's a dumb one. A really dumb one.
My toilet's decided to be cranky on occasion. It doesn't happen all the time, but sometimes after I flush, it'll randomly start running for a few seconds, stop, run, stop, run, stop, and while it's not running there is a small sound of trickling water in the tank. I can only assume the flapper seal is not right, but that's where it gets odd - manually adjusting the flapper by sticking my hand in the tank doesn't work, I can only flush again and hope it'll seat correctly. (Or, um, become very frustrated and give the tank lid a good hard wallop. That seemed to fix it a couple nights ago, when I couldn't get to sleep thanks to it running!)
Can I fix this without replacing the flapper or O-rings, or is it pretty much toast?