I saw your post a while back and found a poor exploded parts view. Didn't make sense so I didn't reply. Found this one now

http://www.poolpartsonline.com/p-359...ent-parts.aspx

and there is an O-ring behind that ring. Thought there had to be. That could definitely be your problem but first, can you tighten that collar? May be enough. Hayward pumps use 4 bolts between the motor and pump housing and every spring I need to torque mine to stop a dribble. I have no idea what that yellow tab is.
Al