There is a kit availabe from BMW for what they call "pendulum shifting" There are a number of plastic thrust washers that disintegrate in the transmission and start to cause problems. The installtion of that kit requires that the transmission be removed from the car and paritally taken down. The longer that the unit is driven the greater tha chance that internal hard parts could be damaged. These transmission are not inexpensive to get done. I would start calling around to trans shops on quotes to have the unit taken down.