If your reservoir is cracked you WILL NOT be able to pressurize the system. You have to change it before you proceed.

While it's said that there are no stupid questions, sometimes it makes a person wonder if the one asking it should really be working on a system as CRITICAL as brakes. Perhaps you should seek out a good repair facility.

 

If your reservoir is cracked you won't be able to maintain pressure to bleed with. I just did this on a Boxster and I think the reservoir is the same part as on my daughter's A4. I had no problems at 15 psi on the Boxster, or any other car for that matter. If you are hesitant you could try 8-10 psi, it will just take longer.

Lou