328 should be a relatively reliable car among BMW.
u should describe the situation to BMW USA, i found USA BMW are quite good in repairing and finding problems.
btw, where are u located? some US BMW are bigger and better than others. Generally speaking, if it is a big dealer, (judging by how many cars they have on site) the better the services. I live in Mid-west and my dealership is one of the largest in the US. (they have 400 new cars on site to choose from, all parked indoors!) They told me they have 2 factory trained technicians onsite to solve difficult problems. They usually do a good job for me.