Hi all,
I could fix the problems myself.
It looks like the problem was with the mirrors. One of the mirror's folding motor gear was stuck. Sprayed WD-40 followed by grease and the folding part worked. I didn't have to open the motor casing as there is a tiny hole that gives access to the gear housing. Then one of the mirror glass's motor mechanism (up/down, left/right) didn't work and I had to disassemble to fix it. If interested, please look at my DIY (
https://www.e90post.com/forums/showthread.php?t=1524591)
I had a PC oscilloscope, so I could see that the mirrors were getting LIN bus signal and the pulse width was changing when I was operating the driver cluster switch. This way I knew that the wiring and programming part is most probably alright.
So finally, everything works thanks to this thread/DIY and the various other youtube videos. The mirror tilt function while reversing is a really nice bonus!