Audi brake fluid

[dpb@Eng (David Bokaie)]

I think I goofed up big time with the brake fluid type on my audi 90 (1988).

Couple of weeks ago, I posted that the grommets under the brake fluid
reservoir is leaking and seeked advise.  I managed to replace
the grommets and the leak  stopped.  However since then I have noticed that 
the feel of the brake pedal had changed. Today I noticed that with light
pressure on the brake pedal, it sinks to the floor indicating a bad master
cylinder.

The brake fluid that I used was the generic DOT 4 type.  The owner manual
says that the brake fluid and the power steering fluid are the same type 
and I remember that there was discussion a while back regarding power 
steering fluid and how important it is to buy it from Audi.  This combined with
the fact that my master cylinder has gone bad is making me suspect that the 
brake fluid is incompatible with the rubber inside the system.

   
Anyways here come the questions:

1- Do you guys agree with my diagnoses.

2- Why Audi is not more specific regarding this in their manual or on the 
   warning on top of the reservoir.  They specify DOT 4 that 
   meets SAE J1703.... which is what I have put in.

3- What is the extend of damage?  How many seals, where...

4- Audi is quoting $290 for the master cylinder and they do not carry rebuild 
   kit.  Are there cheaper sources.  Also are there rebuild kits for the 
   master cylinder. The brake system is Girling.


Thanks,


David