Hi Skyground,

re:
> But I can't replicate what you gave )) After join+rebuild I got 1 single separate curve. The doing
> extrude and got 1 face, but dont understand how to "weld" it to the shape that I have.

You have to use Edit > Trim to cut off the excess area of the new extrusion so that it has an outer trim boundary that matches the edges you want to join it to.

Select the new single face extrusion:


Run the Edit > Trim command, at the prompt to select cutting objects select these 2 edges (there's a little curved one at the top there), then right-click:


Now the Trim command will slice up the surface by the cutting objects and show you the pieces it made. Select this as the piece to discard and right-click again to finish the Trim command:


You'll now have a piece that is ready to be glued back in again using Edit > Join :




There are some tips here for people coming from a poly modeling background, they may be useful:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

Hopefully at some point in the future you would not need to worry about this and filleting would not get stuck when it tries to cross over one of the other edges in the model but right now that can cause a lot of problems. Also I do want to add in a face merging tool that would make it easier to merge together 2 adjacent faces when possible.

Hope this helps!

- Michael