Same problem here. I finally tore into it this evening. Took me about 1.5 hrs to fix it. would only take me about 45 min if I had to do it again. There are 4 resistors that are on the cluster board that looked bad. I re-soldered them since at least one joint looked weak. What do you know, it is back to original brightness. The bad joint was creating a lot of resistance and as a result a lot of heat. Replacing the solder should correct that. We'll see how long it will last. Here are a few pics I took. Take the cluster out, unscrew the black panel on the rear exposing the circuit board. the board just lifts off the rest of the cluster but a ribbon cable is still connected to it. You don't really need to remove the circuit board but I did trying to find the bad area but now I know I did not need to waste my time doing that. I also took the opportunity to remove the clear plastic and clean up the dust from inside the cluster. Here are a few pics. If it goes out again I will probably buy new resistors and try replacing those...what do I have to lose by doing that.
The circles are the back sides of the resistors. The arrow is the joint that I think was the problem. I replaced most of the solder joints anyway, just to be safe.