Dave,
I think you can check the bolts, and tighten if needed, and replace the seizing at the outer end of the spreaders without hauling the boat and dropping the mast. If you need welding at the mast/spreader joint, it will depend on the welder. But I suspect the welds are probably fine, so do the other checks first, with mast up at a mast tower or with a good bosun chair. I think this problem is likely easier to fix than you think, but it's important to get it right and have spreaders and shrouds right, and the rigging well tuned.
Frank