[tsubaki]

Welcome to the site. Nice clean V.
If the transom needs replacing, it will be expensive, usually more than the boat is worth. But given the prices of the new(er) boats may be worth it due to you knowing the repaired condition of the boat.
What your describing is usually dry rot from water intrusion.
Mine showed no appreciable flex doing the bounce test with the motor but when I got curious and removed the cap and started digging, found the only good place was directly center where the motor bolted.
Stress cracks should show up but not always where you think. Look a little farther beyond the transom, like the floor, cap ties and bottom about 2' from the rear.
I'd use the flex of the motor on the bracket as a barometer, also listen for slight popping as you bounce the motor. As far as the "whole thing going", you should see some compression of the transom from the bracket and possible loose bolts before any real problems are created.
Don't base any decisions on one opinion, listen to several people and do what makes the most sence.