Crack in aluminum mast : options?

[Brion Toss]

Hello,
A tricky one. First, if corrosion is a contributing factor, something else is really, really wrong, like stray current or weld sickness, in which case these cracks might be indicative of problems elsewhere.
Next, this sounds like a classic stress riser failure, at least as far as the crack origin goes, but there are lots of topping lift mortises with corners, and they don't all crack like this, so these cracks, once again, might be indicative of problems elsewhere.
Next, drill stops can only do so much. I have a picture, courtesy of ace surveyor John Koon, of a similar crack that had been drill-stopped three times; the crack just kept bypassing the stop. The length of the cracks, in this case, do not speak well for the mast's remaining integrity.
Next, why does the mast pump when going to weather? This is not a good thing. It is possible that the tune is off, and/or that the mast scantlings are off. Tune you can fix, but scantlings, not so much. So if you weld that patch on, you might just be welding in a big stress riser, the strengthening effects of which are overridden by the break-here effects. Have you run the numbers on this stick?
Finally, it is very, very difficult to make a non-damaging weld on an aluminum mast, especially at a location, like this one, that is in a bend-intensive section of the column.
I'm inclined to say replace that mast. But if the numbers come out okay, and if a sleeved section won't compromise efficient bending too much, then a complete sleeve would be a much better fix.
Fair leads,
Brion Toss