A o ring does nothing but preloaded the threads .I find it hard to believe you were a expert reloader when you were eleven years old. And engine main bearings float on a film of oil and you progressively torque the heads to ensure they are flat and square.
The link below at this website tells you a rubber o-ring "May" reduce runout. Meaning if the lock ring is not secured square with the die it can induce runout. So if you do not use o-rings how do you know "YOUR" lock ring is square with your die when it is secured.
O-Rings on Dies May Reduce Run-Out
http://www.accurateshooter.com/technical-articles/reloading/o-rings-on-dies-may-reduce-run-out/
Most press the the ram and the the threads that that hold the dies do line up
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