Interesting.... I tried to reach back and hand tighten the supply line and it was tight, I could feel the water leaking further up from the supply line. I guess I need to take the toilet off and turn it over and inspect it before I start buying parts.
I was also thinking that I should add some dyed water into the bowl and see if colored water leaks out the back to help eliminate bowl seals.....
looks like a pain to take off the toilet bowl. 2 nuts hidden inside the toilet. see manual.
owners manual link