As an update, the shop told me I had a bad PS pump and a bad hose, but they could not get the parts. I ordered the parts online, and they installed them. After picking up the car, by the time I got home, the PS reservoir was almost empty (2 miles!) I took it back in, and they told me it was another hose, which they could not get. I ordered it online (I thought) but it was the same one they had replaced. Today I'm going to the Lexus dealer, who say they were able to get the part for me ($199), so hopefully this saga will end today.