I've got a 2012 Mini Cooper S, and it's slipping, its a bit wet at the bottom of the trans so I think it has a very slow leak. I've read and researched, and it seems that there is no dipstick, and the filler is very difficult to get to? is this possible to do on my own? I'm very handy but all the videos etc. I've watched are really unclear. I'm sure it needs to be changed etc., but right now I want to fill it to see if that will take care of the slipping. thx as always! john p. PS I put R59 in the suffix but not sure thats right.

 

I ran into having to fill my trans a hard way. I'm sure there are others.
R60 How NOT to change the oil - North American Motoring

The title says oil, but I pulled the trans plug by mistake. I think this is relevant because you don't know how much fluid you have lost. Something that came up in my thread was "just put back in how much that came out" but I didn't know how much came out, nor how much was left in.
Posts #25 and #32 might help you if you want to avoid using the top fill plug, and have the "stand tube" in place (inside the pan stick ups where the drain plug is).

Also just noticed you have R59, which you say might be wrong, and didn't say it was a countryman in your post. So you might be in the wrong spot and my info may not help at all.