14 ob limited
If this is the case then the NTSB should be notified, because this is a serious malfunction that could lead to deaths!the master cylinder has two stages to it for the primary reason of having a back up if the first stage fails for some reason. The ABS valve is for sure an interesting possibility given from the sounds of it your master cylinder could be OK and you could still have a case where the brake pressure is dumped if this Valve is acting up.
Report back on the shops findings - you won't be the only one who comes across this I'm sure of that. ;-)