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,
THE RIGHT CHANNEL GOES OUT!
3. WHAT CAUSES THIS?
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,
AND EQUAL VOLUME to the LEFT CHANNEL.
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?