I recently had an injector go on bank 2, so I replaced all three on that bank.
I have noticed on my datalogs that bank 2 fuel trims and A/F ratios are much smoother than prior to the swap.
The bank 1 trims still oscillate up and down comparatively to bank 2.
Going to replace bank 1 injectors very soon as well since my cold start idle is starting to act up.
I only have 50K miles on my 2008 135i, but it looks like the injectors don't last in these cars and create all sorts of headaches from misfires, to rough idle.
Sucks if it's on your own dime.....but only $107 each from Tischer.