Fuel Sender Replacement

Im in the process of replacing the sender units due to fuel gauge errors. Having trouble with the retaining rings that must be removed to access the senders. I have the suggested toll (OTC 6599) and have read that even with that, you must apply a great deal of force.

Im really pushing, even with a 3' breaker bar as suggested by another poster here, but it's not going. Turning counter clockwise.....

I can't imagine anyone getting it off without the tool. Shall I keep pushing til it breaks free...? Just afraid of breaking something...

Advice?