BMW is notorious for being not sturdy. Mercedes Benz maybe a little bit better in that regard.
While Jap cars have a lot of short comings when it comes to handling, and are often very sluggish, Toyota, for one is pretty sturdy, across the board. I had a BMW 520 years back, and it gave me the same kind of problems you had. I finally threw in the towel, and sold it. I bought a Toyota Avalon and it gave me good services. I put in 285,000 miles on it, and it was still running fine when I sold it for $1,000. For the price I paid, I cannot complain. However, if you are looking for handling instead of sturdiness, Toyota should not be your choice. It is just a work horse. Period.