Can I Grind and Paint?

[fathom]

Hey all,

I threw this up on the Facebook group but figured I’d shoot it up here as well. We are starting to really jump into our IV build and I noticed the small area of rust shown in the picture attached. Can I sand/grind and paint this or what is the best option to get control? It doesn’t appear to be significant but considering this is where the wing strut attaches to the fuselage I would like a second opinion.

Also, any thoughts why someone would put hysol on the weld unions? I’m guessing to prevent mositure from sitting in the corners and causing corrosion?