I can't offer much advice on the cleaning part, but I will give you my thoughts on repair/replacement. I was in a similar situation several years ago with a Sony receiver (from the 1980s) which I was very attached to. The estimate to repair was just too high. I ended up buying a nice Aiwa receiver for a ridiculously low price (through Crutchfield). What I got was good sound, all of the functionality that I had with the Sony, and a remote control. No, it's not audiophile-quality, but I'm guessing that your Yamaha isn't either. (If we were audiophiles we probably won't be on this forum.) So I say, spray the cleaner in, rotate the switch back and forth several time, and see what happens. If that doesn't fix it, look at replacements. If you're just using this unit for a sound system (and not a TV, etc.) you don't need a "home theater" reciever, although you could still use one. Yes, it's a shame that everything is now disposable, not repairable.

You want to spray the cleaner in the back side where the contacts are. If you spray it in from the front it will never get to the contacts. Besides, there is grease on the shaft and all you will do if flush the grease out and make the shaft harder to turn.

I owned this unit some years ago. I sold it because the input selector was damaged like yours. It was a mistake, I never found similar quality of sound in other Yamaha amp. Thee bass is rich, short, the treble dont fatigue my ears. I recomend you repair it. I found today a yamaha-natural-sound-stereo-receiver-rx-750 and I will buy it

One of the most common problems on stereo gear that has rotary switches or rotary potentiometers (volume, tone and balance controls). Just dirty and oxidized. Well worth cleaning if you are comfortable taking the cover off and finding the right place. I can recommend DeOxit products by Caig.

I have a RX-V995 if your interested.