Hey, thanks so much everyone! Sorry for the delay in replying, but it's always one thing after another... The last vibrations were due to the front transmission, which was a bit worn. It was repaired and that was it. It's true the wheels also needed balancing, but not enough to cause the car to shake so much. Anyway... In the end, we got rid of the car, since it was always one thing and then another, and certainly expensive things.
Cheers

, and thanks again to everyone!