hello I'm from ft86club actually not a mini owner and I've never actually driven one either, but my friend has a problem with her's and this is where I thought I'd go.
Anyways the other day I was in her car and noticed a shudder every time it shifted. My immediate thought was the tranny fluid. She took it into the dealer and they said that the whole transmission need to be replaced. Should I go through and change her ATF (using the pdf guide) ? or is there actually something seriously wrong with it.. thanks !
edit: and also what parts would i need to replace if I'm changing the fluid and filter.

 

You will get more helpful information if you post more information about the car. There are several different auto trans depending on model and year.

So, post up year, mileage, model(cooper, cooper S, Cabrio, Clubman, etc).

 

year 06, mileage 60k, cooper s with the paddles. thanks for the heads up lol.

 

There is a big thread on here about yourfriend's Aisin 6spd auto. You can change the fluid, but more likely you need to change the valve body too. It is much less $ than the whole tranny, but still expensive at about $1500 or so depending on labour rates and what fluids you use.
Find a good shop that will diagnose and is able to do a valve body swap. Take it there and go from there.