[Asianoak]

Well I'll chime in with one recommendation I haven't seen yet. I originally started looking at the first generation X3s due to lower cost and the fact that I really only wanted the SUV for space. However, after doing research I found that the newer ones do have much better interiors and the amenities make up for any price increase you may take.
with that being said, reliability is a concern with any modern turbo engine, not just BMWs. And transmission issues should also be removed (for lack of a better term) from consideration since so many manufacturers are using the exact same transmission as what's found in the X3 in their SUVs. Finding one that has a fluid change or two really is your best bet when it comes to the transmission but these are not like the ones found in the old e46 3series that failed like clockwork at a certain mileage.
So my suggestion would be to look for a 2011 or early 2012 28i xdrive. these will come with the N52 engine which is non turbo and has shown to be highly reliable in comparison to other modern BMW engines, mainly due to the lack of turbo components and high engine stress and heat associated with turbos. It will have a bit less torque than the newer turbo'd models but I didn't feel as though the difference was enough to warrant taking the risk of additional issues down the line. I think you're in California as well which works in your favor. I'm in southern Oregon and during my search the majority of low mileage vehicles with the features I wanted wound up being in California. I eventually got mine for I believe 22k with 52k miles, fully loaded except the sport package and had full service records from new.