So I got my '93 in October-ish last year, always had a problem with the power seeing, looked here and got a few tips, but none of them applied to my specific issue, which was steering fluid overflowing past the reservior cap, seemed to me there was a block somewhere. My wife and I both work and have two kids, so time is hard to come by, I've just been trying small things and dealing with the leak-my driveway is ruined! Plus, its been too cold to work on so I need to drive to work (20 min away) if I want to do anything and still be able to feel my hands, lol.
Anyways, to the repair.
I had already done a screen cleaning at the sensor on the rack, as well as a flush, neither did anything.
The screen in the reservior was clean, the sensor on the pump was previously removed and capped.
It was suggested to me to try a reservior o-ring, I really didn't think it was that since it was leaking out the top, but it was under $10 so I have it a shot as well, no help.
So last week I removed the pressure line from the pump and rack and blew through it, had flow, not the problem. Removed the rubber return line between the two steel lines on the pass front of the car, hose was fine, tried blowing through the steel line going back to the reservoir-nothing, used compressed shop air slowly, eventually it blew through into the reservior and flowed free afterwards. Re-assembled everything and lowered the car, looked in the reservior and the screen was blown out from the pressure, removed the screen, filled the fluid and no leaks! Steering is a bit tight at idle, but works perfect otherwise and no more pump hum.
Anyways, so it seems that the screen was not flowing enough fluid to the pump fast enough, so it was overflowing past the cap.

 

you have the intellect to be a world-class Lexus mechanic! - good job!