Though I don't recall seeing it in its pure form, the Wikipedia entry says lead styphnate is yellow to brown. If you got slimy green around the cases, it is probably verdis gris from reaction between the brass and salt water, or it may be nickel chloride (which is also green) from salt reacting with the nickel plating on the primer cups or with nickel on nickel plated cases.
Most military primers are not nickel-plated and steel military cases have a varnish on them. Also, military ammo tends to have both primer sealant and bullet sealant, making it harder to damage by submersion. Special ops divers have to carry the stuff without damage, though presumably they don't do this for days at a time.
Bottom line is that military ammo is good bugout ammo from the water exposure standpoint. You can, however, seal your handloads. Nail polish is often suggested, but I don't really know how well it seals. Permatex makes a UV setting primer sealant, which sunlight may be adequate to seal (need to ask them). There are also a number of moisture sealant sprays out there and roofing sealants. There's also a clear silicone-based sealant with toluene as its solvent that's made for repairing wet suits. I acquired some from a dive shop years ago and it looked fine on primers, but I never wound up getting the ammo I tried it on wet enough to challenge its function. Some experiments may be in order.
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