Drip leak from a 2 yr old toilet / bolt
Why would you take the word of the plumber? He installed the wrong parts, which now leak. He also says he knows more than Kohler. Three strikes against him.
How about taking the word of Kohler, who made the toilet and knows which parts work? Wouldn't that be a safer bet? And if you go this route and can't fix the toilet yourself, will you make the same mistake again by hiring the same plumber?