I recently discovered that my Kohler Wellworth Northline Barrington toilet is leaking at the base. After removing the toilet and placing it on sawhorses, I plugged and filled the bowl with water. After about 8 or 10 minutes, drips started to show up on the floor.
After talking to Kohler about my experience they recommended replacing the seal between the tank and the bowl with a part #GP51487 to fix the problem. My only concern is that the leak showed up with only the bowl full of water. Would the new seal be an effective fix or is something else going on? The tank was not filled and so I'm wondering if the seal between tank and bowl would be a solution? Any trouble shooting advice would be appreciated.

did you get down on the floor and look up at the bottom of the bowl to see where the drips were coming from?

Start with a completely desert dry tank and repeat your experiment. As Packy states, you have to get under the sawhorses and look up at the underside of the bowl. You are looking for the source of the leak so you will have to find the leak path, and dry it as you follow the path to the source. It may take you to a sandhole in the china casting. Usually, a sandhole in a toilet bowl will result in a noticed lowered water line in the bowl during periods of non-use.

Also, adding food coloring to the water will help a lot. It may be that whatever you plugged the toilet with simply got saturated and is letting water past, but colored water is easier to trace.