It looks like a bar from a selector switch or possibly even a record bar.
Yeah floyd it's the record bar, the mystery part connects to it. It's part 114 in the diagram.
It slips into part 113, which has a clip that slips into that arced slot behind the mounting hole I point to with the blue arrow.
The flap on the end of part 113 lines up with the deck's record mode actuator.
When the deck's actuator pushes on part 113 and turns it, part 114 also moves, which switches the record bar.