I beleive this is due to the Mexican Palm he planted back in the back corner of his yard. He planted it 2' from each wall. When it was small, no big deal. But now it is 20' tall with a 30" base and is less than 6" from the wall. But it is not directly touching the back wall so neither of us know for sure if the palm is the problem. He is willing to have the palm removed.
Is there some way to push or pull the back wall up against the common wall like it was when new? I was thinking a 2" wide by 3' long steel C-channel as a brace on the ooutside back wall. Drill holes in it every 8". Then drill deep holes in the cinder blocks and screw some tapcon cement bolts in to see if we can pull the wall back so that it once again is touching the common wall. But I have never tried this before and wonder if the cinder blocks can take the stress. They may be too weak and brittle.
Any other brilliant ideas?