So, due to the lack of instruction, I've dismantled the lens to try to see the problem, but, unfortunately, the zoom ring is attached to an internal mechanism, and it couldn't be removed.
I tried to open the body during a few minutes and couldn't find a proper way to do so. The body doesn't have screws! Maybe it is glued.
Lubrication is not the problem as I could observe internally. It happens that the there is something obstructing internally the ring to move upward.
I've read someone who had the same problem in this Bolex 350, but a long time ago and no answers. I guess this camera has this vulnerability as the decades go by.
Does somebody know how a super 8 works in relation to the internal mechanism of the zoom? Any tip is highly welcomed!