Went to bleed my Magura Marta brakes today and the master cylinder seals sucked in some grit and lost all function. Now I know you can't rebuild these brakes but I thought what the heck lets wash em degreaser and all completely opened up no hose. Worked the lever to try and dislodge the crap a thorough cleaning. Blew it out with compressed air then ran mineral oil through the assembly working the lever once again to dislodge all the water and any leftover crap. Put it all back together did the bleed and voila good to go. They feel better than ever.