The hydraulic tailgate system, standard on all US bound E61 wagons, seems prone to leaking and failure. Replacing either the hydraulic ram or the pump requires dis-assembly of large parts around the cargo area to provide sufficient access, involving many hours of labor. My extended service protection plan declined any claims related to this repair. This is also exacerbated by the fact that the hydraulic lines are permanently attached to the hydraulic ram (the part that pushes the door open) and run, in one piece, through the rear trim, above the headliner, through the D pillar housing, and around the rear drivers side access area so that to check the hose for leaks requires accessing all of those areas. To access the pump, remove it, add fluid, or disconnect the hoses, the stereo amplifier must be removed. It is partially obscured by a different set of panels requiring the removal of the rear cargo area liner (drivers side), the vent trim below the window, and a panel against the back seat.

I, personally, have ordered parts from BMW in Germany to retrofit the vehicle to standard gas struts so that the problem will not happen again.