Its clay filled therefore dimensionally stable, made from almost the same fiber diameter as the OEM. The cover of a good glossy paperback novel cover should also work the same way. Of course since this 'paper' isnt resin bonded, will only be temporary .... until the exposed fibers become digested by the water.

Of course you can also use black RTV silicone, apply a bead of the RTV, 'slightly' close the cover plate to ensure 'contact', let set, and after 24-48 hrs, tighten down on the plate. RTV is now used in many applications on automobiles where such paper gaskets were once used ... differentials, transmissions, etc. etc. etc. Just besure you dont get a 'blob' of RTV 'squeezed out' to the 'inside' of the pump.