Spongey Brakes

[DigzTheBeatz]

Recently the brakes on my 89 325ix have started to get real spongey. I only noticed it after coming down the mountain from a day of snowboarding. If I pump the brake once before actually using the brakes to stop the sponginess goes away until the next time I have brake.
I had a couple shops look at it and was told it was probably the master cylinder. I took it to Brake Team for a free inspection and they say the master cylinder looks good and isn't leaking. I took back to Les Schwab for their free inspection. They said it probably wasn't the master cylinder since I get pressure back after pumping the brakes. They bled the lines and said I has a lot of air come out of the right rear. They recommended a flush, which I had them do, and the brakes worked great again. I went to the mountain the next weekend and now my brakes are spongey again. I took it my shop I always go to and they say it is probably the master cylinder. I'm getting different answers from different places and am getting confused. I'd hate to spend the money on replacing the master cylinder if that isn't the real problem. Any advice or suggestions? I found a couple people on here willing to sell me one if I need it, but I want to make sure that is the real problem.

[jlevie]

If the system was fully flushed and air has gotten back in without the reservoir running dry, the probable cause is a bad master cylinder. in almost all cases, a bad seal at a caliper, a problem with one of the lines, or with the reservoir seals will result in a leak rather than air being sucked into the brake system.