Disappearing brake fluid

["John North" <johncnorth@gmail.com>]

My front brakes are out and the fluid is empty.   This happened once
before, a few months ago, no leaks apparent, so I figured I hadn't
checked it in a while and just refilled and bled them.   It has been
OK for months, but now it's happened again.   Could the fluid be
leaking into the servo?   If so, would that indicate a master cylinder
rebuld?   What about the servo, if that's where the fluid is, how
would I get it out?

Any help appreciated.

John North