These are common here in S.GA. My first ? would be: Is the wall stacked, as in each timber/crosstie are stacked on top of each other? OR- are the timbers/crossties "staggered" as in one timber rest on two timbers? I'm thinking (UH-OH) the if they are staggered you may be able to remove the bad one by just cutting out parts of it until it is all out. Placing the new one maybe could be done with driving wedges between the one on top of the empty space and the ones that it rest on. If they are stacked on top of each other you're idea may be better. Thanks, David