I'm trying to figure out why some cast iron tops in my shop are more resistant to rusting than others.

When rust appeared on my old contractor's table saw I cleaned it up and applied protectant. One time I took a RO sander to it, with some rust preventative on the disc. It seemed that held pretty well. I did the same to the bandsaw. When I moved to Florida, rust was a bigger issue and the cast tops required more attention.

Since purchasing the new cabinet saw, I've found the cast top on that requires considerably more attention than the other cast iron tops. So now I'm wondering if it's the metal they used to make the top or if the cast top will absorb protectant over time to the point it will only require attention as much as the other cast tops in the shop.

???