B7100 Transmission shim location

[airheadrob]

Hello, I have a 1983 B7100, I am replacing the FWD shaft inside the gearbox as it has suffered a bit of a catastrophe, I'll post the story when it is fixed. After the gearbox was lifted out I found a shim on the floor that must have come from the gearbox. Would anyone be able to tell me where it would have come from? (photo attached) I can't a shim on the WSM drawing.
Thanks in anticipation,
Rob Hargreaves, Howick, NZ