I recently took my 2017 BMW 2 Series Active Tourer to the local BMW dealership for a 2-year brake fluid replacement. I was advised that the technician was unable to service the rear brake cylinders as the bleed valve/nipple had corroded and was at risk of breaking if too much pressure was applied to remove it. I was advised that this was not a repairable item and that new calipers, at a cost of about £500 each, would be required. For a fully equipped main dealer workshop with highly trained technicians, this seems strange. Are you aware of the reasons why a repair is not offered? Do you know if they can be repaired and where I can find a repairer?