My first question - Has it always done this?
2) Have you tried a new Kohler flapper? I would try that first. Its
inexpensive and will guide you as to what to try next.
3) if its always done this, and a new Kohler flapper doesn't solve then
try the following next.
You say that the chain pull somewhat sideways and you suspect this is
causing the issue. Can the arm from the flush handle be bent so it is
positioned directly over the flapper? If its plastic, try replacing it
with a handle with a brass rod that can be bent into correct position.
Did that fix it?
if not - check to make sure there is no debris or damage to the flange
the flapper sits on.
if not - Call Kohler, see if they can offer a suggestion.
if not - Consider replacing the entire flapper/flange/overflow.
Typically they are one assembly. Not sure about your specific model.
DO NOT - Get the fluid master flapper/flange combo with glue that
sticks to the existing flange. These have never worked well for me. I
ended up pulling it out and replacing the stuff as mentioned in
So - As you can see - Check obvious, try less involved, less expensive
things first. Worst comes to worst replace the troublesome parts and
everything they touch.