It is a toughie. Easy for me because I spent many hours in the signal box - even if the off-peak there was work to do to get the trains to the common platform.
Let's give up another one and a half clues:
Despite this station having more than one platform, during the 60s and 70s (at least) all off peak trains in both directions used a single platform
The station has/had more than 2 platform faces (has now and had then)
Although some peak-hour suburban trains terminated here, the off-peak trains which used a common platform were through trains
Incorrect guesses: Upper Ferntree Gully, Lalor, Mooroolbark, Brighton Beach, Lalor, Werribee