You need to remove the dirt from between the split -- it's going to be very difficult for it to merge when there's soil in the way.

For some reason I feel that may be doing the turgor pressure a great deal of pain.

I followed the other thread, as did Garden Knowm. You should try cleaning the wound up very good, and if the split is still moist it should merge. If not, try roughing it up just slightly; then spraying the area with a water/SuperThrive mixture; then tape the two halves together and leave it be.

It could be interference with the nutrient uptake, so essentially a lock-out of an unusual kind.

But still, there seems to be something else..