Battery I insta acid damage on 730

Flooding the area with any base will neutralize the sulfuric acid crystals locked onto the cast iron. If you use any oily fluid, it will seal off the air preventing rust, but you will trap the acid "salts" on the metal. These can and will draw moisture from the air and "pop" that paint down the road.

If it was me (and it has been before :) ), I would:

1) flood it with warm water/baking soda, brushing lightly as I do, 2) air dry
3) apply some Phosphoric acid to turn the remaining red rust in the area to black oxide which is benign to further oxidation (it will also give a light phosphate coating to the fresh metal in the area). 3) let it dry thoroughly (maybe even use a warm lamp)
4) then sand, prime and paint.

I would use a really good quality epoxy primer here.

The main thing here is to neutralize the acid, kill the rust, and then seal that fresh metal from further reaction with moisture and oxygen.\

Frank-in-Tallahassee
70D // 855

I would also soak, wash the area down with baking soda or your favorite snake oil from the spray can just as an added measure of getting the acid out of any pores.