The mount cannot be replaced. Only repaired. The wood transom is welded to the holder. The holder is welded to the tube.
Fill the cracks with a little black 3M 4200 or Sikaflex 291, then squeeze them together...get creative and make a jig to hold everything together while it cures overnight. Trim the excess away with a razor.
Then cut some black PVC and put a patch over the whole top of the transom holder. I'd do both sides so it is symmetrical and looks nice. Remember to MEK the surface first and to mask off your area that you are gluing. Excess glue turns orange and looks nasty.
Gluing geek since 2007