what specifically is the pump doing, or not doing? these units also supply supplimental vacuum to the climate control system, the main problem i have seen with your model is the climate control has a leak and this causes the pump to run excessively, over time if the leak is not fixed this will cause the pump unit to fail, is the central locking feature locking and un locking the doors? please let me know more about you specifin problems. you can send me an email if you want, to the address below.
Ray
mercedessd@cox.net