OT?: failure modes of a RAMDAC

This is OT in that the piece of hardware that I'm looking at (matrox millenium pci card) is newer than 10 years. On the other hand, any comments on this might be useful for older equipment as well. Here's the scoop: the video card in my home computer suddenly started acting flaky. The image flickers and has diminished brightness; at first I thought that it was the monitor, until I noticed that the area inside the dialog window that pops up when operating the setup menus in the monitor does not flicker and has normal brightness. Aha, cable or connector, I thought. So I tested another monitor. Exact same symptoms on the second monitor. Ok, then a cold solder joint in the card. I extracted the card and had a good look at it. Nothing looks wrong. I put the thing back in and it still had the flickering. Then, all of a sudden, brightness jumps back to normal and everything works fine for the rest of the session. Next day, I power up, and several hours later the symptoms reappear suddenly. I am thinking that the output of the RAMDAC is being severely affected by something that diminishes its swing. As far as I can tell, all colors are affected uniformly. The flicker is random, does not appear to be tied to a given frequency, and seems to affect the whole screen (refresh is currently 85 Hz; changing it does not alleviate the problem). So I wonder if there is some oscillation in the output of the RAMDAC or an internal short that limits the swing or what. Has anyone seen this sort of failure before? carlos.