So clutch fluid has more movement (due to the pedal movement or just how the master/slave work here)?

If you think about it--brake fluid contaminants and moisture settles at the lowest point of your braking system and does not circulate much (if at all) back into the reservoir--the lowest point is also the most important point, right where your brakes/calipers are, so cleaning the reservoir alone is NOT good enough.

As a science experiment, I bled my brakes for the first time in three years yesterday--the front two wheels were fine, but my back two wheels had fluid that was darker/cloudier than I can tolerate. My reservoir fluid was brand new, however, since I've been turkey basting it every 3 months for 3 years.

So mystery solved, case closed. Merely turkey-basting your brake reservoir is NOT good enough. Bleed your brakes folks!

Thanks!