New toilet, keeps running. Help!

[Cantfixit44.]

I am sure I’m just a novice and can’t figure out what is wrong. I moved into a newly built home in October. Our downstairs toilet is a Kholer K39990 I think. It keeps running on its own every hour or so.
My quick research said to replace the black rubber piece under the cap. Tried that to no avail. I’m sure someone else knows what to do?
Thanks in advance!

steve

 

[Twowaxhack]

There’s a thin red seal on the bottom of the flush tower.

Replace it. The new ones from kohler are yellow.

watch a YouTube video of how to replace it if needed.

 

[CT18]

Check to make sure it is seated correctly if it is the one that sits under the plunger type. I have seen those replaced and not put in the correct spot and the toilet kept refilling.

 

[Cantfixit44.]

you guys are so helpful, I checked and replaced the seal and it seems to have worked! I appreciate your guidance