it's been a while but apparently the middle pipe from the abs unit and the valve block bleeds the exces pressure back to the accumilator so this owuld be the first port of call when bleeding is concerened

if you are changing the master then simply plug the pipes when you remove them to stop any possibility of this happening again

bleeding the system is effort but not money, changing the unit means youv'e got to find a decent quiality unit first of the right sort as there are 4 different types