I think part of the reason WOZ seems to be down more is that it's a completely different system than the operators are used to and they don't know how to repair it yet. So it ends up being down longer than the other Stern/Bally machines that they are very familiar with how they operate and how to fix them.

Tim at the PHOF says he can't fix WOZ when it goes down and he has to rely on his distributor to help fix it. I attribute that purely to Tim being an expert on the other games and he's just not as familiar with the WOZ system in order to fix it.

So it's possible WOZ doesn't actually break down any more than any other machine, just that the knowledge doesn't exist yet in the operators to effectively repair it as quickly as the other games they operate so they are down for longer periods of time.

Just a thought though.