Piston valve vs Diaphragm valve for urinal

Hi,
My local church has a few urinals that periodically (2-3 times per year?, maybe more because sometimes problems are not reported to me) run without stopping. The solution has been to hit the top of the valve a few times to get it to stop.

I've had the local plumber look at it a few times. Each time, they just open the diaphragm valve and just clean it out. They say that if the tiny pinhole is blocked, water will not shut off.

The church is on town water and it's possible that we have some old pipes somewhere that is flaking (Church was built in 1962), I don't know. Since we're on septic, I would like to find a way to prevent the water from running.

I was thinking that we should replace the valve with a piston type that is designed for harsh water conditions. If I do this, will it make the urinal relatively maintenance free or do the piston valve have their own issues? I've asked my plumber about piston valves but I get the sense that he doesn't have much experience with them.

With a diaphragm based urinal, how often should one have to service/clean the diaphragm? Is this easy enough that a reasonably handy person can do himself?
http://www.sloanvalve.com/Maintenance_Guides/Flushometer_Identification.pdf

I installed piston flushometers on the urinals at my church.
Those were TOTO, but Sloan makes them too. I believe they are more dependable then the diaphragm versions. And your plumber is correct. It's the little hole that plugs. It doesn't take much.

Has he replaced the diaphragms with the "dual filter" versions? Piston valves need less pressure to operate, but when they need repairing, the only "good" repair I have ever had any luck with was replacing the whole pistons, rather than using a repair kit.

http://www.sloanvalve.com/Brochures/Royal_Flushometer.pdf

The only replacement that might have been done would be to replace the diaphragm. I don't think a dual filter version was installed.

I'm not 100% sure but I think the manufacturer is Zurn.

I'll see if I can positively identify the valve we're using this weekend. Thanks.