Don't even think about an in-place repair. The block needs to be cleaned, stripped down to bare bones, and on a stand where the crack can be repaired properly. It sounds like your best option would be another layer of Marine-Tex, or just ignore the seep and check the coolant level in the radiator once a week- - - - -what's a few drops of coolant leakage to the outside going to hurt in the first place?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!