Re: Why does chlorine and brake fluid react?

First of all, you can't pour brake fluid "on" clorine at STP, because chlorine is a gas, and a gas is not something you can pour onto. I am going to guess that when you say chlorine you actually mean sodium hypochlorite, either in powder or aqueous solution.

Second of all "what actually happens" is a complex question because you are not dealing with a single compound when you refer to brake fluid - it is a mixture of many different substances, although mostly highly refined alkane and silicone oils.

So, in reforming your question into one that makes a bit of sense, mixing most compounds with sodium hypochlorite will result in a breakdown of the oils via oxidation, which what the hypochlorite ion is a strong example of, and oxidizer.

Oxidized oils generally lose most of the qualities they are noted for, stable viscocity, lubrication, wettability.

Chlorine gas is also a strong oxidizer, although harder to provide in a volumetrically dense form.