What "O" ring for a Leaking Honeywell Zone Control Valve V8043l

[ap]

Was hoping someone knows the size/type of "O" ring I need to get to correct a leaking zone valve ... I can see water escaping from the edges of the square cover plate that is held on with 4 screws ... so far the motor seems unaffected and no water damage (lucky) ... also I can remove the motor and I see no water leaking from the ball shaft. I presume a new O ring will correct the edge leak but other than on line I cant source one locally cause I don't know what size etc I am dealing with. If anyone happens to know that would be great - would like to try to find one locally today if possible... local suppliers are happy to provide the entire Valve for $100. but I figure a .75 cent O ring should do the trick. Thanks