Before replacing the section I would look at trying to have a new base fabricated. If you can get a template of the existing extrusion which should be relatively easy you might be able to have a sleave made that would fit it. The other option would be to cut the bottom so that it has a nice clean end, then build a post to support it on.
While these may work, if it was me I would just replace it. But then I tend to work mostly on race boats where the stresses and tolerances are small and any weakness can become disasterous much more quickly. If you do go with a new mast, I would however seriously look at a carbon one. Since a new one is sunck cost anyway, the difference in price is not likely to be all that much more expensive, and the weight savings aloft would be very significant.
You might also want to look at composit rigging for the weight savings, but then like I said I tend to think along racing terms more than cruising.
