bleed it, hold one side of the brake so the piston can't extend, apply oil to the (other) lazy piston........repeat and it should have solved your problem sounds liek the piston is getting jammed in the lever......take the blade and tpa off, and all the hoses and bleed screws, now get a 2mm allen key, poke it in the bleed screw hole until the piston pushes out; clean the piston and inside of the lever body; reassemble and rebleed