If you have a friend who has an MHD wifi dongle and the MHD app, you can basically check the "condition" of the gearbox and see if the shifts are within "tolerance". The only other way around this is to pay for the ZF oil analysis, if memory serves me well, it should be roundabout R500 odd.
After a certain mileage, the clutches basically cant operate without the accumulated friction materials in the "old oil" and this is why ZF wont service a gearbox thats out of spec .
PS BMW will never admit this but what they mean by lifetime fluids, is that under normal circumstance that this fluid will not be changed whilst the vehicle is under Motorplan