Manual, or exploded view, of Aussie 4 speed

I am wanting to check on what washers etc fit on the bolt that compresses the reverse detent spring.
The box I bought has only a thin fibre washer on the bolt, and when screwed right home it seems to compress the spring too much, and the result is that the lever (about 2" long) on the box cannot be moved. When I back the bolt out a bit, it operates ok.

My guess is that there is a washer missing, so I need to confirm that, and discover the thickness of any missing washer.