Are you using a spray cleaner? In my experience, spray cleaners can cause more problems than they solve. I use a needle applicator DeOxit Red. Applying the oily droplets is the best way to clean these types of contacts.
I've had my 976 since March and I've only had to clean it once, so far.

HDMI connections do become oxidized overtime, even when they are plugged in and in use. In the four processors/AV receivers I've had, this has always been the case. I do know the speed of oxidation depends on environmental conditions.

I looked closely at the HDMI ports in the back of my 976 and they appear to be of good quality.