Please Advise: Pre-Amp RIGHT channel OUT

For some reason the RIGHT channel went out on my
Pre-Amp tonight while listening to music.
The Volume control knob was at 9 O`Clock,
and NOT even at 1 watt per channel!
1. What caused this to happen tonight when I`ve been
listening to my pre-amp for at least 4-6 hours a day
for the last 3 weeks?
2. When I put FORCE DOWN on the volume knob,
to turn it up or down, the RIGHT channel COMES BACK!
When I put FORCE IN OR UP, on the volume knob,
4. CAN some contact cleaner spray SOLVE this problem?
5. When I let go of the volume knob, AFTER pushing
DOWN on the knob, the RIGHT channel stays ON,
6. IS this a SERIOUS issue?
7. HOW much will it cost to fix this?
8. My pre-amp is from 1990. HOW much LONGER can I
expect this amp to last?

It does NOT sound like anything is wrong with the preamp's circuit -- so, no serious issue.
More like a contact problem with the volume pot. Contact cleaner spray would be useful -- but you'd have to apply it on the inside of the pot, on the contact surfaces, with the amp switched off, of course. Then turn the volume up & down a few times to clean of the contact surfaces.

Changing a volume pot is not an expensive undertaking -- if it comes to that (you'll have to use the same value replacement pot, of course). It might even improve the sound if you opt for a quality pot!
In addition check cracked solder joints arround the volume controll internally.
Gregm is right that it is probably a contact issue , but it seems to me that the solder joint at the volume pot rather than a dirty contact is more likely to be the cause. Of course, cleaning the volume pot is always a good idea w/an older unit.
We've probably posted together at the same time with Swampwalker basically meaning the same issue.
You guys hit it on the head. That is cleaning and solder joints on the pot itself. Should be a cheap fix, even if you have to take it in for repair. Sean
Sean- that's what i thought when I brought my 20 y.o. top of line Yammie pre in w/the same problem. $150 later, I got a cleaned but not repaired unit back!!! Yikes. Guess who lost me repair business? Too bad, they are only 2 miles from my house.