Yeaaahhhh, I found out what was causing the terrible convergence on the lower left corner !
I was experimenting with some of those strips with metal pieces on one end and sticky stuff on the other that are used to converge the corners of a CRT (thanks to a great guy here on the forum that sent them to me for free, you know who you are
). I got it improved quite a bit, but then I noticed a weird piece of tape on the tube right in that lower right (from the backside) area. Turned out it was "holding" two of those strips, but it failed to do it's job properly, the strips were loose from the tube where the metal parts were. This caused the terrible convergence !
I removed them and it instantly got a lot better ! It's not pefect yet, didn't have more time, but I'm sure I can get it 100% now with some more tweaking with these strips !
You can see the white strips going to the center of the CRT clearly here: