Polymer vs Metal and the usual "We'll see if your plastic gun still works in 2112"

I often see people point out that "metals guns run forever" as a counterpoint to polymer guns. It seems to me like they're forgetting that well maintained/preserved metal guns run forever and ones that aren't, don't.

So, wouldn't the same be true of a glock or M&P (polymer handguns)?

If you're posting random conjecture, please point that out. If you have a job in materials science, point that out, too.