There are old weapon systems we could send them as well - but probably already have.
So yes, we're probably running low on munition.
At the end of the Gulf War, we were down to a week's worth of certain aerial munitions, when the fighting stopped. If the war had continued, we could not have sustained the bombing rates much longer.
I've been out of the Marine Corps for almost 20 years, but I never remember ammunition having a shelf life as long as it was properly stored. In the 1980s we were still using artillery shells, mortar shells and .50cal rounds from the Korean war. I can imagine that there are some things that only be used for training after a certain age, e.g. missiles, but the we were always hoping for a higher allotment of training munitions.
If it’s old stuff we would have gotten rid of anyways, we wouldn’t be running low, would we? That really makes no sense