I would use them because from what you said the rust was on the outside of the working part of the filter.

If you thought there was still moisture in them you can put them in your house oven at warm setting which is about a 150 degrees.

All filters have residual die oil on the metal from pressing processes. The outsides are cleaned after assembly only for painting/labeling.

I don't know if it is always true. Most of the time that I have opened a box the open end of the filter is down. I surmise that its because that end sits more flat on the store shelf and less likely to get dust to migrate into a filter that sits out on a shelf.

Therefore I imagine water ran down around the filters not into them. The paper box kept moisture on the outside surfaces until they dried out.

If the inside of the outer can did rust and have flakes wouldn't they be caught on the outside of the filter. Oil should flow from the outside towards the center/inner tube, I would think.

Maybe some other owners know which way oil flows in and out?

I'm pretty sure there is a screen on the inner part in case the filter medium plugs or deteriorates it will be caught. Plus I think the bypass valve spring works so oil can go around the filter.

Gee, I might have to cut an old filter apart to double check my thought on how these type filters, filter and bypass. I was told once that when an engine is above 20 to 30 mph there is more oil bypassing than going through the filter. They screen more than filter. The engine circulates a lot of oil per minute.

Darn, another question?