MX 110 Troubleshooting

I recently purchased a Mcintosh mx110 z series tube preamp and am having a problem with one of the channels.
Left channel has very low and then no volume when I turn the amp on. If I turn the on-off switch on and off; sometimes the sound comes back on the left channel when the switch is in off position. Then it may stay working for 20 minutes or so before it fades to no volume again.
Not sure what type of problem this could be.

Any help would be appreciated.
Sounds like the caps are starting to fail.
Clean the pots and switches, especially the volume pot. My vintage gear has your exact symptoms when they need cleaning. With power OFF, spray pots and switches with NON residue electronic contact cleaner and exercise the switches and knobs for several minutes each, then spray again to remove contaminates loosened by the switch wipers.
Start with the simplest thing first. Try cleaning all switches, buttons, etc before doing anything else.
Thank you all.

I cleaned switches and pots this cleared 85% of problems.
Tomorrow I will give it another round of cleaning.
Looked over the circuit assembly and see just a small spot of dark goo on the bottom of one of the capacitors.
It's caustic so remove it before it eats into the chassis.
So I finished cleaning switches and pots for second time.

Wow !

I have a beautiful fully functioning tube pre-amp!

Thank you