I have a concrete patio slab measuring 12' x 25'. Over 40-years, I've
used muriatic acid three or four times to clean the concrete.

About 6 months ago, oil-based paint was spilled in various areas on
the slab. I've tried removing the stains with muriatic acid and other
products (a solution of soap-and-hot-water; paint-remover; Ajax;
bleach, etc) but nothing removes the stains. What else can I try?

If the stains don't come out, can I paint the slab? (The slab has a
few hairline cracks). How do I prepare the slab, what kind of paint
should I use, and how would I apply the paint?

(I live in Riverside California (about 60 miles east of Los Angeles).
The lowest temperature may be below 15 degrees and the highest
temperature may be almost 120 degrees).