OK. Good reason to keep it.
I am not a plumber or other pro.
I would feel the seat for any deposits or nicks.
I would use some silicone plumber's grease, and rub the seat and mating part of the tank ball with that. I have a tube of Molykote 111 that I use for O-rings etc, and I would use that because I have it. I bought it to lube the O-rings for my water cartridge filters. If I were buying for just this one time, I am not sure what I would buy. OK, I would buy another 5.x ounce tube of Molykote 111 because it lasts forever, and it can be used for more than one plumbing thing. It is fairly thick/viscous as silicone greases go.
https://www.plumbingsupply.com/toilet-parts.html#tankball has some parts and pictures. Some of the tank balls may be softer than others. Softer would be able to conform to seat imperfections better.
There is another possibility or two. You could get the flush valve replaced, or you could get a flush valve repair kit. The repair glues a new seat onto the old seat, and it replaces the tank ball with a flapper. However going through the
http://m.korky.com/home.php troubleshooting guide makes me suspect that those repairs may not be compatible with the old toilets.
A little refill water every 3 hours is not all that bad.