I'm no pro, but at the suggestion of a friend I checked the oil in the HPOP reservoir. Turns out, even just a few hundred miles after an engine oil change, it was BLACK!!! It was SO thick, that when I tried to hand-pump the oil out of it, the pump created a vacuum and kept collapsing the tubing between the reservoir and the pump. Apparently, just because the engine oil gets changed, it doesn't mean the HPOP oil gets changed?
On my '02 there is an allen screw (forget what size) on the driver's side of the top of the HPOP reservoir. I just unscrewed it, pumped it out and refilled it. Seemed like it was a good idea even without any specific problem traceable to it.