Help: Right channel static/drop out on Stereo setting

I have a Marantz 6300 turntable, 70s RS Realistic STA-90 receiver, and original large Advent speakers.

I have been having issues with my setup where the right channel sort of drops out and becomes very static-y when playing LPs in stereo.

But if I unplug the RCA cables going into my receiver and plug them back in, the issue clears up for a little while but then the same thing happens again...it's become very annoying.

Additionally, if I use my mono button there is no issue either. And this is only an issue for the phono setting, not AM/FM radio etc.

Could it be that the RCA inputs need contact cleaning on my receiver? The system sounds great other than this issue.

Any help is appreciated!

 

I've also noticed if (when it appears to "short" out/static on the right channel) if I adjust the balance knob, I can still hear music from both sides.

I wonder if it could just use a good cleaning.

I would love some help. Sort of lost on this right now.

 

On older equipment, always suspect the receiver controls first. Every button/knob/lever should be cleaned. I have never had a RCA cable go bad.