My 64 Dodge is at the mechanic shop now. Power steering gear box , steering shaft input side.. We need to replace the large O ring that is under the large " nut" . That nut is about 3-4" in diameter and has several slots in it. I expect those are for a special spanner wrench? We have tried a hammer and chisel on a slot and it won't budge. Any idea's on how to get it loose short of using heat? we are trying to do it while it is still installed in the car. Thanks for any help.......................MO