S4 brake problems

[JIM_WARREN@HP-FtCollins-om4.om.hp.com]

Item Subject: cc:Mail Text
     
     My 1992 S4 has recently been experiencing the following symptoms:
     
     (1)  After sitting for several hours, brake pedal chatters on the
          way down (not smooth depression of pedal).
     
     (2)  After sitting overnight, no brake boost initially.  Pedal feel
          is very hard.  Brake boost comes up after 15 seconds or so.
          This happens about 25% of the time.
     
     (3)  Brake fluid and hydraulic fluid levels are fine.  Braking 
          performance is fine.
     
     Is this the pressure accumulator (bomb)?
     
     What is the cheapest way to fix this?  (Dealer wants $400+ for part)
     
     Is there anything else that could be at fault?  I can mail order a 
     new accumulator, but I would hate to install it, pay for it, and not 
     solve the problem.
     
     Thanks for the tech help.
     
     Jim Warren
     Fort Collins, CO