There's an article in the latest Hot VWs (Sept?) on replacing the 
front brake hoses on buses.  When these get clogged up, the fluid 
will get to one side more easily than the other and cause the car 
to pull.  They're easy to replace if that's all you're doing, but 
the metal tubes may also be clogged and the wheel cylinders might 
be shot, too.  It sounds like the rear hoses might be bad, too. 

Also, the disappearing fluid probably means there's a leak
somewhere. 

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Mark Thomas                         | Yet there's not a train I
Evans Library, Texas A&M University |     wouldn't take
(409) 862-1052 / FAX (409) 845-6238 | No matter where it's going
mthomas@tamu.edu                    |   --Edna St. Vincent Millay