Jeff Handy
Pro Handyman, NOT A Pro Plumber
The original problem that you described, which is that only a huge flush of water can lift open the flap for the valve, will not be helped or improved by cleaning up the flap or the sealing face it rests on.
Meanwhile, you should put some penetrating oil all over the bolt that holds the flap on.
That should help the flap to swing up easier.
Then manually operate the flapper many times, to work in the oil and to grind up any crud stuck inside the hinge.
I would not remove that bolt, it looks stainless which is brittle, if you go squeezing that split end and then re-spread it, it might snap off at the splits.
Meanwhile, you should put some penetrating oil all over the bolt that holds the flap on.
That should help the flap to swing up easier.
Then manually operate the flapper many times, to work in the oil and to grind up any crud stuck inside the hinge.
I would not remove that bolt, it looks stainless which is brittle, if you go squeezing that split end and then re-spread it, it might snap off at the splits.