Not sure if im understanding your original post right, but ill play...
So, youre having trouble getting the catches on the backs of the blades to go PAST the o-ring to lock in to place???
If so, have you tried sliding the o-ring down toward the threads and out of the grove, closing the blades, and then putting the o-ring back in place? Then they would really be locked good and tight.
Like I said, not sure if I understand your problem completely.
Derek