Back to the topic: It seems like I found the source of the problem (this time it has to be it).
There is was a HOLE ON THE ROOF
Last Sunday it rained from 12:00pm to 5:00pm. I had the car parked on an uphill. I checked the car at 2:00pm at there wasnt any single drop inside the car ( I had the trim and carpet removed during all week). I checked the car at 5:00pm and it was FULL of water. Just the fish missing.
I tought it was a hole or something that wasnt close to the place the water was found. After some searching with a friend, we removed the roof's stripe and found out a HOLE, just above the driver's area. The inclination there is towards the front. If the car is parked on an uphill, the inclination goes towards the rear, leading the water back to the B-pillar. I watered the hole using a bottle and ALL the water entered inside through the B-pillar
Long live the Italian build quality !!!
It seems like the plastic/rubber stripe at that groove, got a bit loose after two years and let some water slide underneath..
I glued the hole with a special glue for such applications, at my local bodywork garage. If anyone wants to check his car, all he has to do is pull the stripe upwards ( first pic ) starting from the REAR, and check the groove for any tiny holes. When you reach the front edge, dont pull it out, because it has a small ammount of glue there. My hole was 1mm x 10mm, just at the edge where the two metal surfaces overlap each other. I put a circle at the pic to make it clear. I took the pic after applying the glue, actually the hole is 30cm more in front of the circle, but i did the circle there for visibility reasons (the glue is black).
I just hope this nightmare has finally ended.