I had new tires (Yoko) installed on my MPV back in May '07. Around July '07, I started noticing the vehicle pulling to the left. I took it back to the tire place and had the alignment checked and everything was within spec. One of the mechanics said it could bea check valve going bad in mypower steering unit. He added some conditioner, which made no difference. I took it back a few months later for the rotation and had them check the alignment again - still well within alignment spec but still pulling to the left.

Is it common to have a bad power steering check valve, or did I get a set of expensive crappy tires (should have stuck with the Michelin)?