Definitely worth it as it is a fraction of the cost of a rebuilt gearbox. They recommend the oil be changed every 80 000km (if you tow a lot) to 120 000 km - I go with 100 000km as that is safely in the middle. Plus they do a free diagnostic on the gearbox to check filling times and pressures.
If it is too far out of spec (if the gearbox is say on 250k km and still has the original oil or someone has put in the wrong oil) then they won't do the service as the clean fresh oil will make it start to slip sooner.
So best to have it serviced at least every 100k km imo.
My friend took his 240i to ZF for a gearbox service and for the diff oil to be replaced, he is on 90k km and still under motorplan. However some of his figures were slightly above where they'd like it to be and since his car is over 5 years old with the original battery the technician said it is likely caused by the battery being degrade and not being able to provide the mechatronic solenoids with enough power which can cause wear on the gearbox and also lead to the pressure and fill rates drifting upwards.
The condition of the oil in his gearbox is still great though they said.
After installing a new battery and driving for a bit, the pressure and fill rates could come down. I found this interesting as I would imagine the power required by the solenoids to be minimal and that the alternator would provide sufficient power. I would never have imagined an older battery to potentially cause damage to a gearbox...
With the 6HP boxes, 150k km might be too high mileage for the gearbox service to be carried out. With the 8HP boxes they can be taken to higher mileage and still have the service carried out but 150k km is still pushing it and you're likely exceeding some of the limits. Apparently they have done the service on 8HP boxes with around 180k km on them though. With the 8HP they recommend every 80k km to 100k km and suggest doing it sooner than later (so closer to 80k).
I guess it is very dependent on how the vehicle was driven.
