smercernary,
The blade grips should be in-line with each other. If your spindle is bent, I can only imagine what grief that must be causing. Especially if it were to rotate within the head as the head were rotating.

mustang,
Haven't seen anything myself about adding another o-ring. And I would think that the only way to make the o-ring equiped head tighter would be to compress the rubber making it bind as you mentioned. JMO but I would think replacing the o-rings with bearings would be the only real way to make the head more rigid. I'd be interested to hear how it goes if you try it..
Mark