Normally the Flo Jet pumps are very durable unless they are allowed to "run-on" dry for extended periods of time (line cleaners not knowing how to turn pressure off to pumps when removing the faucet).
This could be an issue with the beer degassing prior to entering the pumps. Or possibly temperature issues with your glycol circulation. Why the dual blender? Are you using this to pressurize your vessels? If so, do the vessel specifications allow for a higher pressure (20 -25)? If they can, you could use this pressure to propel the beer all the way to the faucet if your restriction is adequate. This would eliminate the need for pumps altogether.
Scott Zuhse, Instructor
Micro Matic Dispense Institute