I had problems with (just one) loader valve spring when my tractor was brand new. It would freeze in the winter. I finally took the cap off and about 2-3 tablespoons of water ran out. They were made in Brazil, I suspect it was just humid jungle air condensate.
I think I opted to not drill a weep hole, and just replace the air in the cap with ~0% humidity North American winter air. It's been good ever since.
I'd guess Chinese, Korean or Indian air could might be able to that to metal!!