the problem - a single, 50 cent O-ring on the return (middle) pipe.
http://www.bimmernut.com/forum/attac...1&d=1240088299
the fix - new O-rings all round since I'm here.
http://www.bimmernut.com/forum/attac...1&d=1240088299
the massive boner I just pulled.
http://www.bimmernut.com/forum/attac...1&d=1240088299
:( go easy