A few years ago ours started to cycle on about every 15 minutes. I couldn't find any vacuum leaks so I replaced the duck-bill valves which solved the problem. I have easy access to the vacuum generator so it was a quick fix. A year later it started cycling about every 30 minutes. Wasn't losing any water and I couldn't find the vacuum leak. I took the toilet apart and replaced the ball valve & seal, spring cartridge, and the base seal.Its been a couple years and it still holds vacuum for a couple weeks.
Did have an issue last year. After a #2 visit the vacuum generator would not stop running. I kept flushing water and a little more TP and it would not stop running and it wouldn't generator a vacuum. I ended up tearing the vacuum generator apart and found a popcorn kernel stuck in one of the duck bills. We still eat popcorn but try not to swallow and kernels.
David & Carol
Charlotte, NC (Lake Norman)
3700 SCR "Comfortably Numb"