You are looking at about 4-6 hundred in fluid for 5 changes. I'd pass and just run the original fill till it dies. There is no data that supports frequent fluid changed will extend the life of these transmission, in fact if you speak to a ZF authorized service center they will tell you to leave the fluid alone.

Much is said about what BMW means by lifetime fluid and it's really quite simple Lifetime means the lifetime of the transmission not the cars lifetime or a humans lifetime. If you get 90k or 180k there is no need to change the fluid. A few of the later transmission have a service interval but that was added due to the confusion over what "lifetime" meant.

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