Channel doesn't kick in at low volume

After 6-7 years of good behavior, my receiver started having what I think is a common problem but one for which I cannot find any reference:
When I switch it on, at low volume, only the right channel can be heard. After I crank it up to -15 or -10 the sound is back at both channels and at any volume.
What would be the cause for this? Is it something that I can fix myself (eg, dusting inside) or does it need service? I could live with this for the moment, but from my experience (with other stereo equipment) this only gets worse.

Thanks in advance

Bump. Any ideas or suggestions on where to look?

Sorry I forgot to say that I did that check. The problem changed sides, so I decided it's the amp.

In almost all stereos that I had since I was young, after some years I got the same problem. After a few more years there is the static, scratchy noise that comes from moving the volume button. I do not have that yet, but as I said, I need to crank up the volume to get it playing on both speakers. Then it stays. I thought I would try to troubleshoot this problem once and for all..

One more data point that might help:
While one of the speakers is not playing, the sound is fine from the headphones. The receiver is Denon 4308.
Does this provide any hints?

Thanks. I just reset the microprocessor. It took quite some time as I had to save, reset, setup up the network, and re-load the configuration. The problem is still there.

If the problem does not show on headphones then it is not in the pre-amp section.
It is either in the connection from the pre-amp to amp or the amp output. I heard some people using DeOxit to clear up oxidized connections.
But I do not know what connection, so I'd rather not play with an expensive receiver.
Any more suggestions are welcome.

Update for anyone with a similar problem:
After extensive web search, I found 3 instances of the same problem. It looks like some relay is oxidized and needs cleaning/repair. See the following link for such a suggestion:
http://www.audiokarma.org/forums/archive/index.php/t-266060.html

Also called Denon 1-800 support and they said they do not diagnose hardware problems over the phone (I guess I expected that).
On the other hand, the service center, which is relatively close by, was very accommodating. They offered to file my case and, when my turn comes, I could bring the receiver in. Otherwise I would have to send it out for 4-6 weeks.