GerryAZ said:
It is interesting that neither the Nissan online parts catalog nor the exploded views in the service manual show the oil seal on the intermediate shaft. Also, the text of the service manual does not discuss that oil seal. I wonder how the main part of the gearcase is vented.
Perhaps because Nissan deems opening/overhaul of the case to be beyond the scope of their dealer service. (i.e. replaced as an assembly).
Just speculating but it seems reasonable the breather is in fact there to prevent any pressure differential between the TM case and the small enclosed space of the brush housing, so as to not drive seepage past the oil seal into the housing. The rest of the case may be vented by other means.