2005 R52 John Cooper Works Mini Cooper Convertible with back seat latch issues. If you are having mini cooper rear seat problems, check this out. The rear seats on a convertible mini cooper have a two part lock and release for lowering from the upright position. First you turn the key in the lock then pull the release lever. If that doesn't work you may have a problem with the release cable. Remove the seat back from the car. I had to remove the bolt at the base of the seat in the middle and then wrestle them out from the bottom. The lock barrels are then removed from the top and the upholstery is removed with a strong plastic wedge tool. We inspect the mechanism and replace the cover when done
Things to look for - broken plastics, loosened bowden tube hold down, or damaged cable.
Good luck!