To the OP, nothing wrong with buying aftermarket parts for your X, I've done it with my E53 as well as the other vehicles myself and my family own. The key is to do your research before you purchase them. There are certain components that I choose to go aftermarket with. Others I will only go with Original BMW Parts. Things to look into are the components typical failure rate, cost, fit/finish, reputation of the brand (if it is an aftermarket part) and even reviews on the forums or place you are purchasing them from. Also think about the frustration factor. If something aftermarket does end up failing think about how frustrated you will be that you have to replace it again, you will tell yourself that you should have spent a little more on one of better quality, especially if it something that is labor intensive to change.

In regards to the whole parts situation it depends on the shop you go to. We don't discourage customers from bringing in their own parts but we can not warranty them if they fail prematurely. If we purchase parts from one of our distributors/vendors there are expressed warranties to replace/repair them in the event they fail.

If a shop owner were to warranty parts their customers brought in they would probably end up going out of business from the losses they would take. Also it is not a case of "my way of the highway" it is a case of being reasonable. It protects both the owner/technicians who work at the shop as well as the consumer.

Short story as an example. Customer with a Honda Accord had some suspension components replaced on the front end of their vehicle. One of the parts replaced, a ball joint, failed causing the hub & spindle assembly to subsequently fail. The entire hub separated from the front end causing damage to the front fender and nearly caused an accident. When it was determined that the ball joint was the culprit the parts supplier was contacted and they have taken responsibility for the faulty part and as a result they are also covering the entire cost of having the car repaired. I've left out some of the details as well as the name of the supplier for obvious reasons. Not to say this is a painless process but it is a lot easier since we purchased the parts. Had the customer purchased these parts and brought them in it probably would have been much more difficult to receive adequate compensation for the damages.

This example is a little on the severe side but hopefully this helps put things into perspective.

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2004 BMW X5 4.4i-Sports Package-Premium-140,000 Miles