I have a cordless phone / answering machine system at home that's
started giving trouble of late. It's a Panasonic, model KX-TG5433. 5.8
gHz. It came with 3 handsets, which I like because I can always find one
of them and at least one always has a full battery charge. I'd guess
it's about 5-8 years old.

Problem is, two of the handsets have stopped reliably communicating with
the base. I often can't get a dialtone to call out, nor answer an
incoming call. Error message sometimes comes up on the handset display,
saying I'm out of range.

I know I can buy a new phone, but I don't mind tinkering with this one
if there's a chance I can resurrect it. I've run into things like this
befo electronic car keys not communicating with the car lock, TV
remotes not communicating with the TV, etc. Is this a matter of
frequency drift as components age?

TIA for any useful feedback.