Yes that bellow act as a seal for the gear case.
This was a bad design from the Force engineers and they changed it to a regular seal later.
They are N/A as you state, maybe Franz Marine still provide a replacement as he did in the past.
The replacement is expensive and a R/R stuff.
You can try to glue the bellow wite Loctite super glue for rubber. maybe it will work for a while.