We have had a few member's use seacast (and other similar materials). Look in the Restoration Section and look at this post there http://forums.iboats.com/forum/boat...r/295740-how-to-s-and-other-great-information and look at item 7
Now since your transome is in need of work........ investigate further and see if the stringrs are also in need (they usually go at the same time)