Leaky toilet

[Rubber Man]

I have a 2018 Jayco TT with a THETFORD toilet that leaks from somewhere behind the top. I have replaced the water connection, but it still leaks now and then usually after a long flush. I wouldn't think it would be the valve since it's hardly used, but maybe. I'll be taking the toilet out to look at the valve.
Any toilet tips are appreciated.

[Grumpy]

There is a vacuum breaker built into the valve and it may be leaking.

[Rubber Man]

If that's the problem can it be fixed, or will I need a new valve?
Thanks Grumpy