now your brake fluid becomes brown. where does the brown stuff come from. Down at the caliper. Even though there is only one pipe down to the caliper. IF you had a closed room of air would the air circulate yes, why because of heating and cooling. The air would rise and fall even though it is a closed room. Brake fluid is heated and cooled, It is compressed and uncompressed It circulates that why is is brown all over and not just at the bottom....

Here is a test for you... I had a professor who aruged that a car saved gas at 55mph vs 65mph.... do you think you save gas driving 55???

NO, because of the over drive transmission your car does 4000rpms at 55 and
3900 rpms at 65 so you use less gas at 65mph. Its the same with brake fluid. Inside that little tube when its compressed it is swirlling around in flows and eddies....believe it or not