Re: What to do with this crack?
Its a pretty scary looking crack let alone all the wood bolted on.
Chances are they were trying to make the transom hold a motor, period.
The inner core is most likely turned to mulch. I'd look real close at all the of the transom seams and fiberglass corners, look for cracks and past patchwork.
Remove all that wood, remove the upper cap and get a good look at the transom wood and stringers and go from there. With the cap off, you'll also be able to better access the crack and how to fix it permanently.