Toilet runs intermittently. I replaced the flapper and it seemed to work for a while. But I've noticed in the last day or two that it is still running on it's own now and then. Only for a few seconds, but it's bugging the heck out of me. What's next?

The new flapper is frequently the fix but the valve it seats againist can also be an problem. Feel it with your finger tip checking for nicks and crud. Smooth off with a 3M pad or 00 steel wool. Worst case scenario it can be completely replaced for about $10 but a bit of work.

Like Ballenger said... check the flush valve. Most likely the new flapper is not sitting against the old flush valve assembly. Here, we almost always replace flapper AND flush valve assembly at the same time to reduce chances of call backs!

Fluidmaster sells an entire tank replacement kit... includes all of the above plus a new fill valve for about $18.00.

I ithink that is the right way to go at this point. You can change the fill valve at this time, too and hpefully not think about your toilet again for a long time!

Good luck...

MARK