There is another possibility for why the crack will not close. The OP stated the crack occurred when he was trying to enlarge the RR hole and my understanding is that he was running the drill through the hole. Chances are, the drill picked up a sliver and jammed it into the crack. If that is the case, no amount of pressure is likely to draw the edges together so long as the sliver is in there. Having been in that situation in a cabinetmaking shop, I can tell you it is a bit of a pickle. If a sliver is the problem, there is a chance it could be dislodged by placing a wedge in the RR hole to slightly open the crack and then hitting the crack with compressed air from the outside. by the look of the crack, I would guess the sliver is about 2/3 of the way back from the RR entry point. It's a longshot but it has saved my bacon on at least one occasion.