Getting ready to do some E46 cooling system preventative maintenance and wanted to share my experiences ordering parts.

KO Performance: They offered the cheapest parts but they appear to not be an authorized dealer or they're selling gray-market wares. The radiator hoses and thermostat they shipped me had the serial numbers scratched off. They took about 6 business days to ship "in stock" parts and offered very little in the ways of customer service, tracking, and responsiveness to communication. Overall they were fine, but it might be something to note if you're picky about your parts and service.

Turner Motorsport: These guys have *amazing* customer service but their prices are a few percent higher than some of the other guys out there. I got a part that looked to have been subject to a latent manufacturing defect and then went out of town for 3-weeks straight. Doug took good care of me and was extremely flexible. It's a pleasure working with honest folks who will go out of their way to make customers happy. They shipped everything out the same or next business day. I'll happily pay a little more up front for good communication and support from these guys.