Thank you guys,
For r.e.wing fc3s,
I should have been more specific. My secondary air pump (000 140 35 85) works, but I’m still getting P0410 code.
I’ve changed the vacuum lines to the switchover valve (and tested for leaks),
I’ve removed and checked the switchover valve itself. It works fine (no hole in the diaphragm).
I’ve changed the connecting rubber hose between the smog pump and switchover valve.
I've changed the O2 sensors,
but still getting the same code.

Now I have the pump on the bench and is hooked up to a gauge (it’s a combination vacuum / pressure gauge, but worked great for me in the past). I’m getting only 3 psi when connected directly from the pump to the gauge.
I’ve sweet talked my neighbor and borrowed his smog pump (000 140 37 85) . His came from 98 E320 (V6). At a first glance the pump look identical, but the position of the ‘exhaust pipe’ is different (different angle).
When I hooked up neighbors pump to the gauge, it was producing only 2psi. I know he got this smog pump just as a spare. He used it for about two months in his car to make sure it works OK and than took it out and it was sitting in his garage. It still looks brand new.
My next test will be to try to measure actual airflow from these pumps. I’ll have to think of same reliable / readable set-up first.

My question is: How do you know if the pump is good or bad? It runs, it produces what appears to be plenty of air...
Did anybody tested any smog pumps? How much pressure should they produce?
Thank you everybody!
Any input is appreciated.
Mark.