Is there a recommended maintenance schedule for replacing or lubricating these O-rings?

I'm guessing that most owners of waterproof handheld radios are more 'handy' than the general population.

Having a number of portable V/UHF radios, GPS receivers and assorted other bits of outdoor electronic gear, I have had a tiny bit of acid-free vaseline on any gasket or O-ring I could find annually. Has worked a charm so far.

(With today's rubber being what it is, I guess I could safely at least double that interval - but it only takes a few minutes, and the vaseline is effectively free, so...

depends on materials and environment, most people can fingernail them out and push a new one in.

they can vary from self destruct, to immortal service life depending on material, and use.