ABS system failure, brake fluid contamination

I am new to the forums but recently had to replace my ABS system after the light came on and dealer said the fluid was contaminated. First, I had never heard of a brake job costing over $6500 but I am most concerned about what could have caused such failure, especially since it was only Toyota who has worked on the car. I found one 2002 online that had had the same problem. Are there more of us out here?