[Spridgets] brake fluid question

[WeslakeMonza1330 at aol.com]

A controversial question if ever there was one.
 
Firstly what is the Castrol fluid?  I'm guessing it's a DOT 4 or DOT  5.1 
and is called response or something.  
 
DO NOT confuse synthetic with silicone.
 
Assuming the Castrol is DOT 4 or DOT 5.1 (NOT DOT 5 or 5.0) my opinion is  
that it will be ok.
 
Regards
 
Weslake-Monza 1330
 
In a message dated 12/04/2009 22:08:09 GMT Daylight Time,  
ryan.kubanoff at comcast.net writes:

I have a  74 with a bad master cylinder thats going to be replaced 
tomorrow. But now the  question is brake fluid and what to use. I presume that the 
system has  original or older DOT4 although last month when i noticed the 
leak in the  resevoir i topped it off with 20ml of DOT3 (i didn't know any 
better). Today  when I went to pepboys for a quart of DOT4 all they have is the 
castrol  synthetic slm that "meets or exceeds DOT3 and DOT4 standards". now 
i have not  seen any more leaking in the past 2 months so i am thinking that 
my DOT3  addition is still in the master resvoir but? 

Advice needed. do i drain  the whole system and refill with the new castol 
stuff, do i drain just the  master and refill with the new castrol, or some 
other suggestion. 
Thanks  
ryan