Recently I tried with slides again
This time I used quite an old Agfa CT Precisa (3 years now) and I must say they weren't that bad, I mean, the images were ok, sharp and the scanner did not return an error, but some of them (most of them) had weird colours that, and this is the worst part, I was not able to correct.
Also, if I managed to get one of them to its point, I could not use the same adjustments on the next one.
If I ever find a solution, I will post it here for sure