Ok,
First I understand your frustration.
Second, You may want to pull out those parts before your winterize the system or take them out all together for the winter.
Third, They are probably breaking from high pressure or water hammer situation.
Fourth, Don't Modify any parts for the backflow preventer as you will void any protections and warranty for the Backflow Preventer.
If you are unhappy with the Febco 765, buy a Watts 800M4, Wilkins 720A, or Apollo PVB4A. I personally prefer the Watts 800M4 and Apollo PVB 4A because they have replaceable seats for the check valve.
Good Luck.

LI0006121, BPAT0011021, CI0009500