McFarland made a .050 wide carbide cutter, indicated the spacer in . . . and cut a .093 groove for a #029 O-Ring . . . and we'll see if this stops leaks. I might still jam some sealer into the splines before we install the sprocket. Make sure the sprocket nut stays tight, so torque that left hand thread nut good and tight to keep the sprocket and spacer up against each other. Tape the gear threads with black electrical tape before you install the spacer so you don't nick your new o-ring. The best way to install it is: Have the spacer lubed inside the seal, and press(or carefully drive it) in as a unit with cork in the bottom . . . but, you probably knew that already? You can send me your spacer, or I could probably get a new spacer and do it for you - about $20 yours - $45 with new spacer + mail. If it stops the leak - it's worth it.