i'm not a huge fan of brake/clutch cylinder repair kits, i find on quite a few occasions the bore is scored and the kit doesn't work.
cost would probably change my mind, cylinders are usually a cheap item but this is bmw here.
if you have to use the repair kit i would hone out the bore with some sandpaper to smooth it out.
another piece of average news for you is when one cylinder goes, it's possible the other will go shortly. they've both done the same work, same fluid... and now you've introduced a new, back to full pressure cylinder... it's going to test your old slave cylinder.
again , i don't know the prices bmw look for these cylinders but if it was any way reasonable i'd stick both on.
also give your lever and cylinder a good clean, pump clutch up and make sure there is a problem there first.
if everything works and lever feels right...sometimes you see problems that don't exist...guess how i know...