I bought a bench grinder from super cheap auto for like $29. Put a buffing wheel on one end. Comes in handy for cleaning/shining up so many parts on a pinny and even your jewellery (like a diamond or wedding ring) and I clean my balls on the buff wheel and they come up like new and are as shiny as shiny can be. Even the buff paste takes away any spots of rust. I then just sit them in canola oil (cooking oil), soak it for five mins, then buff again. That way no chemicals transfer to your playfield.
Doesn't matter what balls u buy, they all start to rust n pit under a magnifying glass from hitting metal ramps n metal parts on ya pinny.
Clean ya balls every month if u play moderately (a few games a day).
Buff wheel is sooo cheap n does wonders.
