Originally Posted by kvc

You do realise that the ZF isn't specific to the BMW? It's fitted to a host of vehicles from Bentley, Jaguar, Audi and Ford. No need to take it to a BMW transmission specialist - most auto transmission shops are familiar with the ZF. The firmware for the transmission is probably specific to our vehicles and that requires a BMW tool to flash or update as the case may be.
When I inquired about having my 6 speed ZF 'serviced' the average quote was $1000. I did the service myself using genuine parts (gasket and filter) plus the Nulon ATF I mentioned (enough to drain / fill at least 3 times, in order to flush out as much old fluid as possible). This set me back around $300 and about 1 1/2 hours of my time. Most auto trans shops will NOT flush the system out completely, as this requires the torque converter to be drained too, so in most cases all they'll do is drain the fluid they can from the pan (about 3-4 litres), drop the pan, change the filter & gasket then add some new ATF to the old fluid that's remains the torque converter. A bit like only draining half your motor oil and adding new to old... I would be inclined to ask what they plan to do with the 'service' they're offering and if it includes completely emptying the torque converter of the old ATF.