I spoke with Eastport Spars and Rigging, and they suggested that a weld is likely the way to go. Of course, they were responding to my verbal description of the problem. I'm very leery of having it welded.
Currently, the crack is tiny. It is about 1" long and basically follows the curvature of the compression sleeve/mast joint for the lower shrouds. Other than this spot, the mast seems to be in very good condition.
The mast has welds in numerous locations that have held up all of these years. The masthead is welded on. The hounds for the forestay and backstay are welded. All of the winch pads are welded on. The compression sleeves are welded into place (obviously, one of these failed).