What I was told, regarding the German ammo, was that some of the cardboard was not quite up to spec (slightly acidic), and caused corrosion where the brass contacted the cardboard. It was restricted to the immediate contact areas only; you’d have corroded rounds all around the perimeter and clean-as-a-whistle in the middle.
Green corrosion can usually be wire-wheeled off; if it’s turned pink, look at salvaging it for components. The pink supposedly means that the zinc leached out of the brass and only copper was left, which could cause case failure on firing. Real shame; people sought that German surplus almost as intently as Australian for its accuracy.
The Portugese battlepack ammo, on the other hand, apparently did get wet along the way. OTOH, if you can find Portugese ammo on machine gun links, that stuff’s clean and reliable, though it seems to hit a bit low.
I went thru all 10 cases of 50 battlepacks, plus the cases of blisterpacks, and they’re 100% dry, clean and useable. The cardboard hasn’t deteriorated at all, so I left it in-place. I also checked all ammo cans and they’re 100%. I have 360,000-rnds for 8 calibers; a LOT of crates, cases, cans and boxes, but all is okay. Spent 5hrs on it, today.
Thanks very much for your tip and advice.