this reminds me of the time i tried to do my brakes on my 318is.
tried but that 1 front wheel (the second one i was doing) was dragging like the brake was on!? think i ended up taking em apart & back together again like 3 times. I gave up & put it back to stock. striker ended up installing em for me..
so it tuned out to be this 1/2 a mm bit or bump (a casting imperfection) on the back of the hawk b.pad. I never noticed it. also before total defeat i had a stripped rotor holder screw, striker had come down to get that out, cause i couldn't do that either so it was actually like a 2,3 day process of aggrevation before total failure
The bad news is that I found oil in the rear plug holes on the passenger side. crap.
Welcome to the wonderful world of the 540I. Gaskets aplenty that need replacing on these beasts. I did the intake manifold and valley pan gaskets on mine, which turned into a bigger adventure that it needed to On the upside, I'd bet that I could do the intake manifold gasket job pretty quick now.