Gas Tank

I've got a leak. It's only running when over half a tank, so it's
probably that
"donut" joint. The shop manual from the library isn't very clear on
this, so
I've got some questions in case it isn't that simple.

Should I assume it's the donut? Should I get one from a dealer and
have my favourite shop install it?

In the book, what is that tube coming down from the filler pipe? Could
it
be leaking instead?

The shield keeps me from getting a good look from the street view,
should I assume it also means I don't have to worry about sabotage?

Will the shop be able to fix it without dropping the tank? How about
with the fact that they are not into Subaru in general?

Nils