Not sure how many folks here have one of the Coolscan 8000 or 9000 models. I was fortunate to pick up a Coolscan 9000 in 2009 right before they were discontinued. Have scanned hundreds of rolls of film in the years that I've had it, and noticed that the results didn't seem to be as nice as I remembered.
Stumbled across this web site:
Started thinking maybe my mirror was dirty. Following the instructions above I very carefully opened up my 9000. Man was the mirror dusty. It was that micro fine dust that gets like cement, stuck to everything. So I VERY CAREFULLY removed the mirror (it's really fragile and mirrored on the reflecting surface, so you can't touch it at all). To clean it you have to flood it with distilled water, and a little lens cleaner, soak a lens tissue in distilled water, and with the surface soaking wet, gently swirl the wet tissue ever so lightly on the mirror surface, never actually pressing the wet tissue to the surface, then flood the mirror with more distilled water, and blow dry with bulb blower. After a few repetitions of this process, the mirror was again sparkling clean. Re-installed everything as per the instruction above, and happily the scanner still works. I noticed the difference in the scans after cleaning. Compared to the dusty mirror, the clean mirror gives more tonal gradations in the midtown areas of an image.
So if you have an aging Coolscan 8000 or 9000, it might be something to consider.