i have the blue dot too, then you have to put these mysterious and exensive washers!?
at the end I put no washers and all 6 bolts the same, black ones that have less threaded part, they seem stronger.
normally there should be one f another type, with more tread on it and green or silver colour, but never understood where exactly? near the blue dot?
I don't have any vibration from the diff, but maybe with the right bolt in the right place it would be better?????
BTW I have a complete M3 subframe with arms, carriers and M3 brakes. so for me the M3 dct shaft was the best, had only to shorten to the right length and mate with a 335i gearbox flange (look at realoem for the bolt pattern mm there are 320d auto that have the same flange you could slavage from)