--I may be able to help with the rubber expansion bolt problem.
--Clearly the Kohler toilets are useless junk. The handle mechanism on mine is very touchy and hard to adjust. The toilet doesn't flush well or efficiently. But my real problems started when the Kohler toilet seat broke. I've replaced lots of toilet seats but the hidden aluminum tube that holds the toilet seat bolt inside the porcelain body was a new one for me. The corrosion that locked the steel bolt into place was a challenge. I cut the plastic toilet hinge off, but the steel bolt was another matter. I appreciate the suggestion to hacksaw the bolt head off, but I was wary of scuffing the porcelain surface where there's little room to work, so I drilled out the head and twisted off the remnants. As others have suggested, once the bolt head is gone, the rest of the bolt drops down into the internal void. The suggestion to drill out the alumninum receptacle and insert an expansion bolt/insert was interesting, but others have pointed out the difficulty of finding that bolt in just the right size. In addition I was wary of drilling out the tube and fracturing the porcelain. So I used a hollow wall anchor inside the aluminum tube. Fasten the seat down with a drywall screw and a washer and you're done. Incidentally, I put wheel bearing grease around the original Kohler bolt that I put back in the undamaged, threaded aluminum tube, hoping that I'll be able to get the bolt out easily next time. Good luck.