New to forum - Looking for gasket for this check valve

[TAZ427]

I'm looking for a check valve cover that would fit the 'squarish' windowed check valve w/ 6 screws (not the round 8 screw windowed check valve) I've got a small leak in the one that's a return from my solar heater (the one closest to the house.)

https://photos.google.com/photo/AF1QipOg6eLUJ9SwVOOn_Sxb-R4G4D4HfrN27aWPGYWq

Any help would be appreciated.