As many of us I had problem with PS pump. No whining but very little power.
Two or three year ago I did complete reseal. Had feeling it helped a little but one year ago the the pump stopped supporting the steering completely - it worked without any wining.
Did complete flush even with cleaning formula. Didn't helped.
Ordered new Maval pump from rock auto. Changed in April and the steering started to work as it should. However it started to leak in June.
As I had some thoughts about valves which were not addressed anywhere and having two pumps, I started some tests.
1. I cleaned the both valves in the old pump as I did not when resealing - it didn't fixed the old pump.
2. I switched the valves from working pump to the old one - it didn't fixed the old pump.

So final conclusion is the not working PS pump is not the matter of PS pressure switch, seals, valves (main and supporting).

BTW. I ended with moving the bearing and the seal underneath from my old pump to Maval and it seems the leakage stopped.