Zenith AM/FM radio loses signal.

I have a 1959 Zenith AM/FM table top radio (I believe it's model 845, but not sure). It's played fine for about a year, but recently when I play it on FM, it doesn't lock in a station unless I adjust the tuner. Once picked up, it will periodically lose the signal again (without my having touched anything). When that happens, I have to ever so slightly turn the tuner again to make it right.

The tuner feels tight (no excessive play), and the sound is otherwise good. Is this a sign of a pending electronic problem I should address (a failing tube or capacitor)? I don't know the radio's history, and am not sure if it's ever been recapped.


Thanks,
Joe