When i was testing an auto micra before i replaced the brushes with some from an alternator. They seemed to do the job, they needed soldering on etc and i cant say if theyd last as long as the original ones but maybe worth a try.
I seem to remember but im not 100% (so i could be wrong lol) that there maybe a part number on the brushes themselves, which might help you track them down and buy them seperatly, as Nissan will only sell you the whole unit.