Not certain if you know this or not but the OEM ones from BMW DO tend to corrode.

I didn't know that. I just like the look of the aluminum running boards.

I did too UNTIL... I went to a few used car dealer lots. Even the ones on the CPO vehicles being sold at the local BMW dealership showed very poorly. I still like the look but the poor cosmetic durability made me decide to skip them. I have been thinking about buying a used set off eBay and then power coating them black which would allow them to last longer and would look good on my black-on-black truck.