In the Goto options you can select Section and Heading as a criteria to GoTo
but I have found that this is not the easiest way to navigate quickly around
a document.
Have you tried the Document Map under the View menu? Give this a try, some
people love it, some hate it.
When you say the numbering is custom, exactly what does this mean?
The GoTo and Document Map will work with the built-in numbering systems of
Word, such as those found under the Bullets and Numbering regardless on how
you have customised these format-wise. If you have designed your own
numbering system these will still work so long as you have applied an Outline
Level (under the Paragraph function).
Other tips for fast working navigation around a document, Shft+F5 will take
you to the last point of edit, even after shutdown. Also the Back and Forward
arrows on the Web toolbar allows for navigation to a certain extent.
Hope this helps
DeanH