I'm very surprised the rubber line on the high pressure side even lasted this long.
The P/S system generates pressures around 200-300psi near steering lock. The pump itself if held at the lock position can generate nearly 1000psi before it fails.
The normal hose you used it bound to fail. Probably right in the middle of a turn! Get them replaced with the proper units immediately.
Yes you should use the P/S cooler.
Also remember the P/S system uses DEXRON/MERCON not P/S fluid...
