About a decade ago I did an experiment to test the story of detectives who sprayed their concealed carry guns down with WD40 and wiped them off at the end of the day and ended up eventually with dead primers in their carry ammo.
l directly sprayed WD40 on primers in .45 ACP, 7.62x25, and .38 Special cartridges, a full magazine or cylinder worth of each, sealed them wet in a zip lock bag, and set aside an equal number of dry cartridges from the same boxes of ammo, and tested them at the end of 2 weeks. Of the WD40 sprayed cartridges, ONE fail to fire, a few weak ejections with my 1911A1 and CZ52.
WD40 is not a sure fire primer killer. It's not good to live ammo. Depending on time exposed it can weaken or kill primers and powder depending on how good the seal is around the primer or bullet.