your prolly better off bleeding new fluid all the way through... keep bleeding it till you get the new fluid out of bleed nipple, will be much lighter in col
i got a lazy one way valve in some tubing for mine couple of years back, saves messing around pulling brake, loosening nipple, retightening, releasing brake a billion times
after your done, clamp your brake lever in with a cable tie over night, really tightens up your lever.... assuming brake pistons in good nick and not binding.
every few thousand miles I strip brakes and pump each piston out a few times while chocking up the others with bits of wood. also brush off all the crud from the pistons. if you dont do this regulary you get 'lazy' pistons that don't move as much as the others. also clean up the pins the pads slide on with abit of fine emery, then coat it with copper slip / grease before reassembly. i think there is some pretty good guides on youtube that go through all this in detail...