2002 Prius ABS warning light...AGAIN

Last week my ABS warning light came on. I took it to a mechanic (who I trust but is not a Prius-specific mechanic) who said warnings are coming up for the anti-lock accumulator and hydro boost motor. However, in July 2011 I had these both replaced (to the tune of $1700). The work was done by a Toyota dealership. I ended up taking my car back 4 times after this work was completed as it kept having braking issues. They replaced the shim kit and bled the brakes. And eventually they replaced the master cylinder (this they did under warranty bc there was no way I was paying them any more money). At no point did they seem to understand what they were doing. (Along the way they broke my windshield and killed my battery.) Finally by November 2011 my car was driving normal again. And then the warning light and high-pitched alarm went off again last week. I talked to Toyota Corporate who suggested I call the dealer to do the work since technically the accumulator and motor just ran out of their one year warranty. But this is the same dealer that didn't seem to know what they were doing last year. Has anyone run into this ABS issue and had work done other than replacing these parts? Has anyone had it happen twice and have suggestions as to what is going on? I appreciate the help.