Lesser Masticore does not have a -1/-1 counter on it.
Steps
Activate Grinding Station by tapping it and sacrificing Lesser Masticore.
When Lesser Masticore dies, its persist ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it due to Curator Beastie.
When Lesser Masticore enters the battlefield, Grinding Station triggers, untapping Grinding Station.
Resolve the Grinding Station ability from step 1, causing target player to mill three cards.