Master cylinder failure is common so I am told. I had to replace mine in 2013. Chrysler did not have any and Mercedes wanted a $600 deposit. When they got enough orders, they would produce a run of them. Well, thats great except the car is not driveable until then. Ordered a rebuild from Cardone which with duty(live in Canada), core charge, currency exchange , worked out to about $200. It has worked fine since. The part # is a1113128.
Don't know if this is of any help.
Deanbob