Okay, before I start, I'm not a noob, I've done plenty of work on bikes and brakes for that matter. I've had pretty mushy/spongey brakes for about a year now but decent enough to ride the trails behind my house. Recently, I found myself with some money so I thought I'd do something about them so I bought an OEM Master Cylinder Piston and Seals, Brake Pads, and a Steel Braided Brake Line. I installed all of this, bled the crap out of it, only to find out that brakes felt the exact same as before. (I know how to bleed brakes) I got curious and took the caliper off and realized that one piston was doing the majority of the work. The other would move but not much. I then pushed them all the way in and the "bad" one wouldn't move at all after pulling the brake lever. I know this needs replacing but can this cause mushy brakes or is it something else that I can't think of? I thought usually a bad piston in the caliper made the brakes stick. I just can't logically think of why it would act spongey. (Btw they aren't leaking fluid and the rotor isn't bent).