Brake Bleeding

[montmil]

... Tons of muck and brown crap, that did not get flushed out surprisingly...

Brake fluid is hygroscopic; it attracts moisture. That nasty muck most likely contains some water that has been emulsified with the brake fluid. Brake fluid does not cause rust. It's the... well, you know.
Rust in the area of the thin, rubber 'dust shields' can be a result of using a car wash power spray to clean the bike. Big, bad No-No as there are many spots on the Airheads that will permit high-pressure water to enter. Milky, water-polluted gearbox lube is just one similar concern. Save your quarters for the Vegas slots.

Flushing the entire brake system annually will go a long way towards preventing a repeat occurrence. The chore is much less time consuming with a handlebar-mounted MC that the dreadful under-tank MC's. Lucky me -I have both styles.

[Barry]

Brake fluid does tend to be taken for granted and neglected. BMW recommend an annual change but that was based on DOT 3 fluid. It's generally accepted that DOT 4 is good for 2 years which is what I've been doing without noticing the fluid being too bad.  How many cars get their fluid changed every 2 years ?

Although Brake fluid absorbs water it's not an immediate problem as new fluid also contains corrosion inhibitors. In fact one of the specification tests brake fluid has to pass is the ability to resist corrosion when contaminated with water.  The problems occur when the corrosion inhibitors run out and boiling point temperature aside that's the real reason brake fluid has to be changed.  I doubt the lowering of boiling point is the same issue with bikes as it is with cars.

[Bob_Roller]

I flush the brake systems on the bikes once a year, only takes 10 minutes per bike .

I use  1 quart, 1 liter to do 4 bikes .

[DerekM]

I'd say flushing the fluid has been neglected...

[Ed Miller]

Tons of muck and brown crap, that did not get flushed out surprisingly.  

Trust me, we're not surprised.  

[arvo92]

I'd say flushing the fluid has been neglected...

Nice thick paste. You can brush your teeth with it!