Vintage imported pachinko balls

[Tazo]

I have a few questions regarding pachinko balls...

1. Are they all steel? Or are there some stainless steel versions?

2. Are the vintage imported balls chromed or plated for corrosion resistance? Are the new ones?

3. If not chromed or plated, what is done to prevent corrosion? I imagine just the oils from being handled multiple times a day in the parlors was enough, but now that these machines are in private hands and played a lot less frequently, is rusting a concern?

4. I was thinking of buying some vintage engraved balls on-line. Are there any tips on what to look for or stay away from in the ads?

5. If any of the balls have corrosion, should they be thrown away or just cleaned?

FYI, I purchased a vibrating tumbler in anticipation of cleaning up the parts on my machine, as well as the balls.

Thanks for any help. I was not able to find a thread that had all the info in one place, just piecemeal info in posts. If there is a post that already has all this info, please point it out.