[TK in LA]

To remore the ring I've used two different methods. First I found a piece of steel bar stock laying around that was about the size of the slot width, ( I may have had to grind it slightly?) and wide enough to go into both slots (across from each other) at the same time. I made it long enough to stick out of the filler hole to allowed the use of a Crescent wrench to turn and remove the stubborn little rascal. The second option is similar. Using the other of the first tool and grind points on both sides of the bar big enough to dig into the metal ring (by taping it in with a small hammer) but not big enough to damage the threads in the tank and not to small to slide into the tank. (You're making your own easy out) Granted these aren't Hi-Tech but you normally only need to use it once or twice?
Hope this helps?