Danke fuhr Ihre Antworten!
Yes, I have original 19 inch alloys and I also have a orginal set of 18 inch with winter tires. I have not done any experiment with those, since they also only have about 3mm of thread.
I have read the topic about the "Standplatten" and that does make some sense. When the tired were freshly mounted, I left the tireshop about 5 minutes later and she drove absoluty vibration-free on the Autobahn at speeds between 80 and 120 kmh. Unfortunately it was just a short drive. Only after 6 hours of standstill the problem came back, but after drivin the car for 30 km on the autobahn it was still there
I think this is the plan:
1) Check for visual wheel/tire runout, best when the car stood still for a while
2) Check and clean the Auflageflächen
3) Do some experiments with the tire pressure
4) Check what the 18 inchs rims do on the car.
If then nothing has been found:
4) Change the querlenker. Good ones "only" cost about 80 euro per side and no allignment (vermessen) is required.
5) Have the car realligned, since the lenkrad is off by 3-5 degrees anyway
6) No idea, we will see by then...
Thanks again!