How Did Front Wheel Bearings Rust?

The '65 Formula S has been going through a three year restoration (sandblast, rotisserie, paint). This week when I went to replace the drum brake wheel cylinders I found the passenger side spindle bearings looked OK after washing them down in gasoline (photo #3), but the driver's side look like they became rusty somehow (photos #1 & #2). Granted, the "chrome" dust caps (as you well know) in the parts stores don't fit well, even after having warped them a little bit out of round so they don't fly off. But still, with all of that sticky red grease covering everything, I just don't understand it.

The race on the driver's side is beat up a little in one area which covers less that 25% of the circumference (see photo #4). The race on the passenger side only has a little dark "birthmark" looking thing in one spot (no photo).

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