@Slamfire do you have any insights regarding the lifespan and degradation characteristics of primers?
When I asked a Naval Insensitive Munitions expert about the lifetime of primers, he said, with respect to gunpowder, primer lifetime is essentially forever. Forever is a very long time, but then, if the design lifetime of double based gunpowders is 20 years, there are a lot of things what seem forever compared to that. Essentially the lifetime of ammunition is determined by gunpowder stability, not primers.
If you look at this document:
Percussion Primers, Design Requirements. Revision A
https://apps.dtic.mil/sti/citations/ADA092511
you will see that high temperatures dud out primers. The USAF developed primer compounds that lasted 3000 hours of storage at 400 F because their standard priming compounds were duding out at 200 F. I would assume that the standard lead styphnate priming compound found in our small arms, should be kept below 165 F temperatures. That temperature is a common high temperature requirement for DoD small arms and ammunition. Therefore, you can assume the commercial primer formulations will be viable in long term storage of 165 F.
I have no idea of the shelf life of the lead free primers. I do know the old chlorate primers would dud out with time.
Primers have a shellac coating over the primer cake. Organics will dissolve that shellac, but from dudding tests conducted by others, it was hard to dud the primer that way. That is probably because, primer cake is soluble in water. And few oils have water in them. I bet that a water bath, following a WD40 attack, will dud a primer, but I have never tried.