Not exactly, will fit, but P9 bigger pistons may change feel of brake . They take slightly bigger pads too, theoretically better
Re leak, when I was doing this a lot (replacing rusty pistons in UK) often I'd reuse the old o ring twixt sides, new ones were wrong thickness.
Also remember some bolts being supplied with shank too long so bottomed out without actually being tight
Between these one will fix your leak but old bolts and o ring surely will