Once again, Paul, I cannot thank you enough.
I am trying to fix broken supports and flange rings.
Rings I can even get remade from aluminium plates, but supports are trickier. At this point, I'm trying to find some chemical to clean aluminum from oxide and corrosion, but without losing more material.
So far I tried citric acid bath and rust remover, but that didn't work.

I took broken supports to the welding shop, but they were unable to help, apparently their electrodes could not bond to the alloy those supports are cast of.
I will try brazing later, if it fails I will have new ones made either by having them cast from a 3d printed plastic models or have them CNC machined.
On the bright side, the powder coating for the frame and group cover is finished:

Looking good with those terrific vintage knobs and manometer!

I was trying to repair aluminium spupports today, I used Durafix brazing rod. I think it will work once I get the hang of it:
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I had to fill the hole and than work the joints, I think I was successful, but I screwed it when I turned the piece so I could work on the inner side. That actually melted the joint.
I do think that this method works, though, becausr the filler material bonded firmly where the hole was, I couldn't remove it with pliers or chisel it out with a screw driver once it cooled.