Its a bit of a pain, but take the snap ring off and take the plate off. I have done it numerous times. I clean my accumulator every so often. Then you can put some heat on it (not too much) and I would put vise grips on it and see what happens.

67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 14.82 @ 94 mph
69 GTX (clone) - build in progress......