[pikfish]

It does look like something to take a careful look at. More pics would help but it looks like the stringer/transom bond area is showing signs of delaminating. This is a critical area of strength especially on an outboard powerboat. I think you also have a bracket? Which would add to the loads imposed on this area. One test I would do is put your finger on the cracks and have someone bounce down on the motor. If you feel movement in the crack get more concerned. Also take a careful look at the joint between the floor and the transom. This having been said if the core materials are sound then grinding and rebonding would fix you right up.