Thanks Dude, that sounds like the right thing to do.
In the meantime i opened it up again and found this plastic thing that holds a piece of copper with 4 lips on ti to make contact with the rotating body. i thought "that must be it! theyre not bent enough to make contact" so i bent them gently...
So, i bought a 50mm 1.4D on EBay and it doesn't work.
It seems like some kind of electrical connection problem because if i twist it in some angles it sometimes picks up the connection and then it works for a few seconds before the angle changes again and i kinda have to wiggle it to make it...