Ted, Impressive vessel. Graupner have gone bust it appears, so grabbing a new Decaperm or two NOW if it will fit and you can find a pair might be wise.
Obviously your vessel is not a hobby sort of item, or we would simply advise fitting a more common geared unit. Purchasing a direct replacement is really what you need considering the considerable sums of money being invested in an operation such as yours. Using something else to replace this unit (both sides would need doing assuming it is a cat??) might mean a redesign of the speed control arrangements and what have you. The cost of two matching NEW decaperms would not be great considering the risk of failure in the cold place and the ensuing loss of data and research time.
I would not risk a repair given this. I would under any other circumstance (fishing bait boat) say "glue it back up and strengthen with a good Marine Epoxy two-part filler"
Ashley