moisture and salt will find a way inside over time
100% correct.
I have two approaches that may (?) help with this.
One, I remediated the existing corrosion at the spreader tips, put on two coats of paint, and then when putting the rig together I coated the tip-pockets (and the monel seizing wire) with TefGel. That "should" help keep the dissimilar metals from getting too intimate.
Two, spreader-tip inspection has a high place on my annual/spring to-do list. Right up there with inspecting halyards, standing rigging, partners/mast-boot, etc. So by this time next year, those boots will have been pulled off and reinstalled. I don't like to "not know" what's going on with the things that keep the mast upright...