2014 Countryman S with JCW leather seats owner here.
The driver’s seat shifts ever so slightly forward/backward when braking/accelerating, but not all the time.
Dealer spent several days, replaced parts, picked up the car yesterday but problem still exist.
Anyone experince the same or is this unique to my Mini?

 

Not exact same problem but I find every day or two, my seat is high and I need to pump the seat height level 2-3 times to get it to bottom out. I'm the only one who drive the car, it boggles my mind!!!

 

I'd be requesting a new seat, I don't think they are technically adept at fixing those things with parts only. Assuming you are still under warranty.

 

I have the fix for that, Holy Water!