I did my transom with seacast and the only way you would be able to use it is to cut the top of the transom off and dig all the wood out with a chain saw and long drill bits. i don't think you could inject sea cast it is way to thick. If I had to do it all over again I would use the seacast. it is lighter and stronger than wood. Go to www.transomrepair.com and check it out. and as for the crack a little glassing before you pour will take care of that. it cost me right at $380.00 to do my transome with no more worries about rot.