mc wrote:
FM stereo receiver, vintage 1973, has a noticeable background hoise
(hiss/white noise) on FM stereo regardless of the incoming signal level. It
disappears completely upon switching to mono.

Is this normal in a receiver of that age? If not, what components are
likely to be deteriorating?

Nothing wrong with it, other than it should have been thrown out 20
years ago. Why are you still dicking with old recievers. Don't you have
a girlfriend or a life?