This is an excellent machine. It's basically the KitchenAid version of the Whirlpool PowerClean, the only differences really being the HydroSweep arm and the stainless steel interior. Get a replacement upper arm assembly and that thing will shine like new money.
As far as the leaking, I wonder if the supply tube for that upper arm is causing water to be forced down in areas it normally wouldn't be, such as the bottom of the door. Crazy things would happen like that when WP used the tower feed to the upper arm rather than directly, and the bladder that sealed the lower arm to the tower would leak and spray right at the bottom of the door, causing water to spew out.