Re: Do we have BMW Tech knowledge in T/C
Bimmers are fun, but can be frustrating. Other than yours is newer than any BMW I have ever owned, I probably qualify as a (former) BMW tech. I worked on them professionally (but retired from that profession in 1988.... so no late model experience), and between my brother and I, we have owned 62 Bimmers over the years. I only have two now, and one is a parts car. My driver is a 1983 745i (Euro model) factory turbo car with over 320,000 miles on it. One of my sons still has two; a 1980 Euro 635CSi, and a 1991 850i. I would never have owned even one unless I could work on it myself. Same with the V12TT MB that Sherri drove for a while. Way too expensive to have someone else work on them. Fortunately for me, I love working on MOST German cars.
The newest one I have ever owned is a 2000 MRoadster. It was Sherri's car, but she decided she wanted a Lexus SUV instead. We have plenty of other "fun" type cars to drive, but nothing that handles as well as the first gen MRoadster. I did very little to the MRoadsters (we have had two), but did replace some plastic cooling system parts with aluminum aftermarket. I doubt an aftermarket expansion tank is available.
Sadly, BMW uses way too many plastic parts. They will distort. They get old and crack; or break. One of the few times I had a BMW break on me while out of town was a radiator neck that just suddenly snapped off two states away. Fortunatly, there was just enough of a nub to score around, and re-install the upper hose. Still kind of a scary ride home with three young children. I was rasing my kiddos as a single dad at the time.
You really should join bimmerforums. Lots of good info. One "good" thing about Bimmers, is that if one e23 (first gen of 7 series) has a malady, soonner or later almost all of them end up with the same issue. On early 2002's it was the 10 spline output shaft on the trans that would shear. On the e23 it is the HVAC system. On e28, the dreaded shimmy from too soft lower control arm bushings. I suspect on your 13 year old Bimmer (you didn't say what model it is) that most everyone else with an 06 of the same model that has comparable miles, will have experienced the same issue.
I used to use maximillian importing for parts, but they are now more expensive that most others. Pelican. Just spend some time looking. Once you get the part number, take a shot on ebay. You never know. I have scored some very hard to find Euro only parts for my turbo car.