This is a question we get often when it pertains to performance parts or maintenance of performance related parts and the answer is a solid, “It Depends”.
Our general rule when it comes to installing parts brought to us by the customer is that we will perform the labor, but we will not warranty the work if the part is defective. There are many things that can go wrong when a customers brings us a random part for their BMW. There are many cheap aftermarket parts for European cars that can be found on eBay with no brand on them. They will simply be labeled as “Generic”. These parts are cheap to buy, but tend to fail within a few months of installation or not fit as generic no brand parts are built with the cheapest metals, plastics, and electronic components. As a business we avoid this by sourcing our parts directly from BMW or the OEM manufacturer, because we warranty our parts and our work.
Another issue we have encountered with customer supplied parts is getting the wrong part or getting a part that doesn’t fit properly. On BMW, Mercedes Benz, Land Rover and other European makes there are mid production year changes where if your car was built early in its model year your car will use a different part as the same car built later in that same model year. When we order parts from BMW we supply them with the car’s VIN number and production date to make sure we get the correct part.
When we take in a BMW with customer supplied parts we also take a risk. That if we run into any of the issues listed above we are left with a disabled car on one of our lifts while we try to get in contact with the owner to find a solution as quickly as possible. Until a solution is found we lose time as that lift is tied up with a disabled automobile. That is why as a business we are reluctant to take cars with customer supplied parts.