Hi, I have colored stucco on my home, and it has been 12 years. It has
never been painted. I plan to hire someone to paint the stucco with
the original color. There is an area where the wall has some mildew
stains on it. After I kill off the mildew, is there a product that can
be mixed with the paint to help repel water? Or something that can be
applied after painting, such as a water sealer?

Anyone has experience with Okon PaintBooster? http://www.okoninc.com/productPg-PaintBooster.asp.
I heard mixing paint with any water repeller may weaken the paint.

I plan to use either Dunn Edwards EverShield or Sherwin Williams
SuperPaint. Which one is better for exterior stucco?

Thanks