Toro 5800 pump Heads wearing out

2015 demo sprayer I do believe . Having pump issues .

 Getting quite the collection pf pumps and heads . Originally the heads wore through ,slightly  after warranty and Pump was replaced with a refurbished one from the dealer .There was mention of a possible casting issues with heads . Great back in business . 

 second pump going in I do believe .

Second pump failed( 850 +- hrs) to and we received some heavy duty heads for repair at 850 hrs. No Idea why this keeps happening . Is it just bad luck or more faulty heads ?Below are pics of the heavy duty heads that blew on pressure side (1056 hrs ), Last 2 sets of heads were blowing on the suction side .  

 Frustrating .... Yes!!!!Before this issue all sucking side O rings were replaced even installed a filter before nozzle manifolds on pressure side . Same as the new sprayers have now . 

 Replacing the suction side hose before installing back into machine all valve holes clean out very well and new O rings installed on them . 2 odd ball valves installed in the proper location as per manual even asked a few Toro gurus to be doubly sure this time . 

Going back in for the fourth or fifth time . My crossed finger pic is all I got till Toro can figure this out if not I'll see you in 250 hours + - . Sales mans wants the old heads to send back apparently. Most frustrating part is that its all speculation of what's going on . Obviously there is an issue some where that needs investigation on either end . These pumps are suppose to be bullet proof from what I hear ( as you can understand that I'm a non believer at this point .) I've heard of only a very few pumps having the same issues as we are .

Marked and recorded in service records .

We use a pre mixing tank before its loaded into the sprayer . Sprayer cleaned and  flushed out after use .