Yes, Goblin Builder can repair walls.
Since my design project is finished, right now I'm trying to catch up on a few things, like Ambassador Applications and such. Once that is done I'll be working on updates to the supplement and trying to figure out our spellbook builder so that it can be updated as well. Those are the most important things I have. That's why I've tried to build some time into our schedule so that they can be addressed before the next set is started.
I have an image of the Goblin Builder on my desktop, but it was too big to attached to this forum post. I figure once we're working on the Supplement I'll be assembling all the cards that have had functional changes so they can be more easily identified.