Checking Gear box oil level FDR 1572

[marrmanu]

Just picked up a FDR 1572 and want to check the gear box oil level.
The owners manual states.
"Check the oil level in the gear box by removing the plug in the top of the box. Add oil if necessary into the biggest plug at the back of the box. Do not over fill!"
This does not clearly explain as to what level the oil should be. I believe it should be to the bottom of the large plug in the back of the gear box?
Is this correct?

Thx Mike

 

[imnukensc]

When it starts running out of the large plug hole at the back, it's full.

 

[marrmanu]

When it starts running out of the large plug hole at the back, it's full.

Thanks, as I thought, need to add oil.
By they what is the small plug at the bottom for?

 

[GeoHorn]

Draining it for a complete oil-change.