toto aquia flush valve leak

I have a toto aquia that has leaked from the tank to bowl for a long time. It was installed in 2008 by a licensed plumber.I have replaced the flush valve twice with factory parts under warranty. Still leaks. I am puzzled by the blue adjustable slide on the valve. The seat appears in good condition and I do have a new one that I haven't yet installed.
What am I missing here?
Al