So today, having cleaned the clutch slave from all the crystalized fluid/moisture stuff, below - some corrosion on the outside of SC body but inside bore in shiny good condition, piston just have discoloration:
And the engine side of it, after several cleaning "sessions":
The clutch line form MC to the SC was previously flushed until clear liquid came out. Torqued SC by feel due to location and inaccessibility. Next the brake fluid went in, the vac pump went to the service port of SC and fun begun... Actually it went pretty fast, got all air out and lever feels harder than before, reminds me of the Magna after installing a Vesrah heavy duty clutch springs, definitely harder than when I bought it.
Noticed a lot of squealing while pulling the lever so I had to take it apart. Found an acorn (??) nut on the pivot screw:
and, just for kicks, looking at the brake lever... guess what... no nut (typical by now..):
Long story short, I ended up with 2 locking nuts (from my stock) for the levers. Looking at the brass piece that has the boss for the MC pushrod, there was ribbing/rough surface on the one side:
Which, after removing with some 1000 grit sandpaper, greasing and reinstalling, took care of the lever squealing.
And now I have a working clutch. Moving on to the brakes next, let the fun begin..