Brake fluids and rubber parts

[Enrique Claure <spaninc@ceibo.entelnet.bo>]

The Dot 3 vs Dot 4 thread has been beaten on this list like an army drum.
However, I have never seen much arguments of Dot 4 Castrol GTX vs X brand.
I feel that in order to comply with DOT 4 chemical and physical specs, the
composition of the fluids must not be all that different between brands.
Thus, Dot 4 for MGs is fine but sticking to a brand seems an overkill
unless some one can pop up chemical formulas and concentrations that I can
look at. Enrique