On the subject of what causes the fluid to turn a darker colour- here's an interesting thread (including a reference to an OEM bulletin)

Reasons why brake fluid would go dark fast? - Bob Is The Oil Guy

Nothing to do with moisture, which nobody has yet explained HOW it gets into a sealed system.

 

Again they are talking GM brake fluid only!! I have never used that product.

The clear product mentioned in the thread will also turn color. It's hard to believe the brake fluid is dissolving the rubber but maybe so?? That is the first time I have ever heard anyone thinking that? And it is just a theory. I would think that would be the first thing checked when selecting a fluid.

I don't see bulletins from any car manufacturer/brake supplier talking about this? So I can't really put any stock into that answer.
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Clubairth-

with all due respect, at least please read what's been said in the posts above and the links provided before dismissing things out of hand.

You've made some rather absolute statements in several of your posts- yet provide no credible data to back it up. The particular statements are repetitions of commonly held beliefs that appear to be myths or outmoded practices that date back to earlier technology- such as the much debated holy grail 3K mile oil changes.

1) You said: "Again ALL cars absorb water into the brake fluid." Please explain how this happens.

2) I asked: "Could you explain the physics of why (supposedly) contaminated fluid changes the feel of a brake pedal?" You have yet to respond.

3) You've stated that brake fluid in plastic containers absorbs water through the container walls, and provided a link to a manufacturers site. I provided a picture of that same manufacturer's product being sold in plastic containers. The recommended Jaguar OEM fluid is made by Castrol. Their product is pictured in your link, also in a plastic container. WTF?

4) You maintain "......the color change is from the moisture causing corrosion" yet this phenomena is observed in vehicles that have sealed plastic/aluminum master cylinders or calipers. Again, how does the moisture enter? A search of the interweeb looking for credible reasons for the colour change reveals very little data on the subject, except for repeated mention of the GM bulletin which advises that the change is colour being leached from the seals. Please provide some substantiation for this not being relevant and for your position that it is indeed due to moisture ingress.

Thanks- I'm just getting tired of this discussion going in circles.

 

There are plenty of places for tiny amounts of water to enter. Mainly past the pistons and their seals (which will only be partial, though pretty good) and the threads etc on the reservoir. Again, they'll be partial seals.

 

Jag-

If you were to remove the cap, you'd see there's a gasket that seals it at the top. Cross that one off the list of possible leakage points.

Regarding the piston seal theory. The fluid pressure can reach into the hundreds if not thousands of PSI. Surely if there was a leakage point, the fluid would exit at this point as opposed to atmospheric pressure moisture entering.

 

No gasket seals completely.

You're ignoring that tiny amounts oover long periods mount up. The huge PSI you mention does nto stay there long.

Presumably (I think rather obviously) the piston seals are pushed very hard against the place they need to seal during the high pressure. What occurs when there's no pressure is another matter.

 

OK, an update on my original posting (re: bizarre brake feel):

Taking advantage of the awesome weather we're having in the midwest this weekend, I installed a new set of Centric rotors and EBC Redstuff pads.

I'm QUITE happy with the results! Brake feel is normal. Braking power is what I expected it to be.

Seems Motive Products shipped me an incorrect adapter (or has the wrong part number associated with my 3.0L S-Type) with the power bleeder I bought, so new fluid is a few weeks away. Really looking forward to having this all squared up.

 

Mikey,
Not to throw gasoline on the smoldering embers of this discussion, but I think I figured out how moisture can enter a totally sealed system. Try this on for size, In the caliper the circular seal scrapes down the walls of of the caliper (which are actually honed with a cross hatch pattern more on this later) essentially squeegeeing the fluid off the walls as it goes. The seal is hydraulically sound because it uses the fluid trapped in the spaces honed in the cylinder wall to provide a strong cohesive bond between the seal and the wall. It works because of this microscopic film of fluid left on the metal. Of course when the piston retracts the metal is exposed to the outside air. I know there is dust boot protecting the walls from the macro contamination but does not and cannot seal completely. So at this point a thin film on fluid sucks up whatever moisture it can (Which I bet is very little, but not zero.) Now, when the piston rides over that area again, the fluid now contacts the contaminated film and they swap molecules again probably not a great deal. Now this process is repeated thousands of times throughout the years and viola! you have contaminated fluid in a sealed system. So thats my theory, for my next trick I will explain why bread always falls jelly side down, and why whenever your butt touches the toilet seat the phone rings..(takes a deep bow…)