I have an 06 with the same problem.I checked with the dealer both in Canada & USA and they would not admit to any design problem.
My own indi.mechanic found the broken part and it was PLASTIC on metal...I am hoping to get the part when I return to Florida next month.It is the
front passenger side slide rail and costs approx.$250.
With all the complaints I have read about with these roofs,it really burns my ass the way BMW is handling it. I will let you know how it works out for me.