brake hydraulic system expert needed

[Dave Glubrecht]

The hydraulic assist for the brakes quit abruptly on my 90 90 20v.  Upon removing the resivoir cap I found the fluid to be low, so I added some.  What I added burped out when the car was started and the fluid is foaming.  Not just foamy, but comtinually expelling air.  The pump also started groaning like there was air in the system, which there is.
  At this point all that I can think of is to check the return likes for a leak that might be letting air in.
The steering still seems to work fine.
  Anybody have any other suggestions? 
  Dave G