Which control unit? There's the hydraulic control unit (HCU) and the electronic control unit (ECU).
The HCU has the valves. 99.9% of the time the OEM (BMW in this case) will only sell the entire sub-system, be it the HCU, or ECU or pump and will not allow the dealer service dept to repair, just replace.
Sometimes they only allow the entire ICU (which is HCU, pump and ECU) to be replaced. They do this out of fear that some one will screw up a repair and cause an accident.