Turning the guide pin 90 or 180 degrees will sometimes take care of the problem. I think this is what Ken meant by "eccentric" - that the pin is either bent or wider (less worn) on one side than another. Generally the key block has a thick cardboard shim glued to the bottom. Removing a layer or two of the card works initially on new pianos. Once this has been removed, though, and if turning the pin or replacing the guide doesn't cure the problem, I don't know what is left, besides the old business card under the keyframe trick (good to get through that concert).
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