Leaking Watts Backflow Preventer

I have a Watts 919 backflow preventer on my irrigation system. It is leaking out the bottom through the relief valve. Most of the advice I have seen states that there is probably debris in either the 1st or 2nd check valve. I've taken both check valves apart - no debris and the rubber parts and seats are in very good condition. I also took apart the relief valve and again the rubber parts and seats look good, with the exception of the diaphragm. It is not cracked or broken but the material on one side (away from the valve seat) is "crumbling." Sorry, don't know how else to describe it and I am not familiar with how it should look. Could a bad diaphragm also cause the leaking? How about a weak spring in check valve #2? By design, check valve #1 has a much stronger spring than #2.

 

Backflow preventers should be certified each year by a licensed inspector. This is not a DIY job. Occasionally there will be minor repairs needed that the inspector can do on site. These are inexpensive by vital to assure the device is functioning properly. I think I have had mine repaired twice in 30 years. My city sends a reminder letter with a list of certified inspectors the homeowner can choose from each spring. If the inspection is not done and the inspection form is not received by the city, the entire water supply to the home will be shut off.