[RobbiZ4]

The o-rings named above are exactly the parts I use for this purpose. The required quality is NBR70, forgot to mention it. This o-ring is so small, that it can be lost while trying to mount it. Buy some spare rings in addition!

BMW will not support you as they don't sell these parts separately.
3.4x1.0 mm NBR70 is the exact size, 3.3x1.0 NBR70 can be taken as well for it. TopHydraulics might deliver them as well, just ask Klaus for it.

The BMW dealers strategy is easy to understand:
1st, they don't have any experience (way better: no clue)
2nd they start to replace the most expensive part
3rd If it doesn't improve anything, they never unmount this part and won't take it back, U have to pay for their faulty decision
And so they will continue to melk you...


Btw, in general your BMW invoice seems to be ok!
They charged the complete harness and their time to mount only the right side. So far no fraud /deception.
But it's a pity that they didn't mount the complete harness. Don't throw the 2nd part away (the one with the 45 degree tape line), as the hydraulic hoses on the left will break sooner or later as well!

Your problem with the hydraulic cylinder on the right seems to be completely independant of your former hydraulic leak! And it's in line with the explanations I got fom Klaus Witte, TopHydraulics about weak seals in the cylinders.