Hey guys it is at the base of the mast. Masts don't break there. I absolutely agree that it is corrosion related damage where the expansion has caused the "weld lines" produced during the posrthole extrusion process to crack.
But I do not see the need to shorten the mast. Get the base out clean it up get a GOOD ali tig welder to weld the cracks and then refit the base. Winding some carbon fibre / kevlar string and epoxy coating the base can not hurt from a strength point of view providing the top is water tight. But I think I would not bother preferring to leave it so that I could make a regular visual check on the welds.
A raised mast step would work too but I suspect the cost would be higher. Mind you it is a steel boat so a raised step would be easy to do. ?