In the 2 and a half years I had my 07 M6 I never had an issue with the hydraulic pump. It's something you can't really predict. The only gearbox component I had an issue with was the Clutch Position Sensor, which was R7k from BMW and about R1500 to replace by an Indy mechanic.
If you have concerns, I would suggest getting it either to BMW or to a specialist that knows these gearboxes well and have them check it out. Come to an agreement with the dealer/owner of the car to have this done. Personally I don't know of anyone on this forum that had that specific problem, but I may be wrong.