At exactly 120 km/h and through the steering wheel, I'd check:
1. Front brake disc runout - warped discs cause vibration at specific speeds
2. Wheel hub runout - even with balanced wheels, if the hub is slightly bent youll get vibration
3. Control arm bushings - worn bushings can cause speed-specific vibrations
Start with the brake discs. Put the car on a lift and spin the front wheels by hand, watch for disc wobble.
had this exact issue on my F21. turned out to be a slightly bent wheel that wasnt visible to the naked eye. the balance machine showed it as balanced but the wheel had a tiny lateral runout.
ask the tire shop to check wheel runout, not just balance. they need to measure it on the car with a dial indicator.
also check your front thrust arm bushings (also called tension strut). theyre a known weak point on the F20 platform and when they wear out you get vibrations and vague steering at highway speeds. cheap fix too, about 100 EUR for both sides.
