on the new style the pressure relief may be built in or could be it is relying on the orbital valve to have a pressure relief.
are you sure the old style is no longer available? tvh maybe?

if you're not getting any relief when steering goes to stall point then it will break that coupling every time.

The coupling is plastic, on the old style pump (Rexroth) there was a pressure relief, on the new style (Casappa) there aren't any signs of a pressure relief.

well then i would double check the pressure relief valves and make sure the system is not set too high causing it to lock up. It may be exerting too much stress on the coupling causing it to break.

One other thing important to remember is to lube the coupling if it is all metal when installing, if there are any rubber parts then do not use regular grease, i would use lithium. If you are installing it dry that may be causing premature wear weakening it.

Thanks for the reply. Both parts I've replaced are from my local Cat dealer.

2 things
if you are using aftermarket parts....dont...
use OEM parts

second is check the relief pressure and make sure it is not too high
steering should go into relief at the stop, you may have an orbital valve problem too.
relief pressure should be approximately 1161psi