Mattax said

That's a disk brake master cylinder - cant tell which casting from the photo but they can be very hard to find. Prices of the correct ones for fixed caliper (4 piston) A-body aer quite high. I bit the bullet a few years ago and finally got one.

All glycol based brake fluids absorb moisture. This prevents any bubbles of water from forming, and up to a point, prevents rust from forming.
I bleed the brakes on both vehicles every Spring or so...
With increase moisture absorbtion, the max temperature a brake fluid can handle decreases. Most of us don't get the brakes that hot so normally wouldn't notice. Dave Mapes is just one person I know that found out that old brake fluid and road racing are a bad mix. He had soft brakes as the race progressed. :eek:

Silicon based brake fluid does not absorb moisture. If moisture gets in its going to find the lowest location in the system and settle there. It's also slightly more compressible, or can be. For most purposes it is quite good and a side bonus is that any spilled won't harm paint. The US Army tested it a number of years ago (reports can be found on the interweb) and now use it for most vehicles.

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