That's the test, pressure on the pedal and if it sinks it's faulty. Do it with the engine off otherwise it's inconclusive between the MC and the booster, with no boost the pedal should be very firm and have no movement. Toyota calls the pedal movement after the pads and shoes engage "reserve travel" I think and the spec is like 3mm. Sounds like to me it's bad.
'91 Pickup - Imelda / '08 Tacoma TRD - Donna
'09 Kawasaki KLR650
'98 Rhygin Juke SS / '12 Gunnar Rockhound 29 / '16 REEB Dikyelous
"Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty. Nobody is able to achieve this completely, but the striving for such achievement is in itself a part of the liberation and a foundation for inner security. " --Albert Einstein