Soggy transom
Soggy transom
A complete rebuild of the transom is probably a bit too much work for most boaters. If you just want a quick and dirty "don't want it to get any worse" temporary solution, you might want buy a can of spray foam to inject into the lowest hole. Remove all the screws first, allow to dry as best you can, and the foam will probably come oozing out all of the holes as it expands and forces out any remaining water that occupies hidden voids in the transom. Once the foam has fully set up, you can gouge out a little of the foam in each hole and re-fill with Marine-Tex, gelcoat or 5200 until you figure out your next move. Certainly not a structurally sound repair, but should buy you some time and allow you to use your boat in the meantime.