I recently fitted mud flaps to my X3 and found that they didn't fit as well as I would have expected of OE BMW parts.
I fitted the fronts first, using the correct mounting holes and the tape that is fitted to the flaps and assumed (yes, I know!) that they would be a perfect fit However, in a very short time the tape pulled away from the wheel arch leaving a gap of maybe as much as a quarter of an inch!
Being aware of this when I fitted the rears I approached the task differently and made sure to correct any of the fixing points that pulled the flaps away from the wheel arch. I ended up having to use washers as spacers on the fixing under the car on the left side flap and on the right side I had to re-drill the mounting hole under the car. By doing this I was able to get the flaps to fit perfectly.
Now all I have to do is take off the front ones and refit them using the same approach.
