Zurn Aquaflush leaking only as the flush is ending - Help!

Hi, I have a Zurn Z6000 Aquaflush and it only leaks as the flush is ending and it stops leaking after the flush is completed. This page shows the Aquaflush: http://www.zurn.com/operations/aquaflushsense/pages/downloads.asp .
Should I replace the vacuum breaker valve?
Do I disassemble by first unscrewing the spud coupling, followed by the coupling at the vacuum breaker? I assume I dont need to unscrew the tailpipe coupling, right?
Thanks for any tips!
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Hi, I have unscrewed the tub nut and the spud nut to loosen the vacuum breaker tube, but I cannot slip out the tube so that I can change the rubber vacuum breaker. Does anyone know how I can slip the tube out? Do I need to unscrew the brass bolt that is attached to the toilet bowl? Or should I rotate the valve body up? I tried to rolate the valve body upward, but it is really tight and I hate to break anything.
Here are some pictures:
http://www.sopmedia.com/sopguest/toilet/DSC03276.JPG
http://www.sopmedia.com/sopguest/toilet/DSC03277.JPG
http://www.sopmedia.com/sopguest/toilet/DSC03278.JPG
Any tips?
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yes rotate the head up or take it off all together,replace the vacuum breaker then put it(flushometer) back on the flush tube

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ps thats a comercial toilet couldn,t hire a plumber?

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I have fixed it by pulling the old vacuum breaker out through the little gap that I have between the vacuum tube and the flush valve body. The breaker is made of rubber, so I squeezed it and pulled it out.
I then installed the new vacuum breaker by stuffing it through the gap and seating it inside the vacuum tube.
Thanks!
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