Here is the key... Two important things to be aware off. Figment of the spoiler. Oem will fit like a glove non oem might, but if non oem doesn't and there is extra pressure required to keep it in position then you could have a lifting problem caused from these forces. Cleaning is very important! I have a non oem large lip spoiler and the profile on the ends is not the best. There is no way tape would hold this down. But the rest is ok so I do have a little lifting just on the end area. If this problem was throughout the profile there would be a serious problem to keep it on with just tape. So oem you will be fine with just the tape.

 

Also with the OEM there is a sweet spot where it will mount with minimal lift. Too far forward and the middle will lift, too far back and the ends will lift. Do a test fit, adjust as necessary, and then mark where the ends, middle front, and middle back will go with masking tape.

 

Great comments. Thanks

 

Thanks. The 530i although a nice car didn't have the power I needed, plus the years and the mileage was increasing so I decided to go 550i and it's a great car as well that I'll keep for a while.