I just installed a JCW grill in my 08 Chili Red/White MC this morning and experienced some scratching of the top of my bumper cover when reinstalling the stock chrome trim. This part, purchased from Outmotoring, had the correct BMW part number on it for my model, which I double-checked before even taking the part out of it's bag. I was aware of the potential for scratching of the bumper cover after reading several posts about this problem on NAM, and attempted to use the utmost caution, to no avail.
The problem, I believe, is a manufacturing size discrepancy with the JCW grill vs. the OEM chrome grill. I base this on the fit and ease of removal of the lower trim from the OEM grill, vs. the JCW unit. When removing the trim on the original grill, the fit could be described as a consistent, loose fit. However, the installation of the stock chrome trim with the JCW grill is an INTERFERENCE fit. There is absolutely no way that the trim will gently slide under this grill, as it does with the stock part, and snap into it's retaining clips. The fit is so tight that the clips are probably superfluous.
Paint damage is inevitable! Installers beware!
I love the look of the new grill, and it should reduce underhood temperatures, as it has substantially more opening area than the stock grill. This is something for the MCS owners in particular to take into consideration, given all the underhood heat issues out there. In the meantime, I think we need to get together as a community to make Mini/BMW aware of this problem and get it resolved.