I'm not that familiar with the 123 automatic climate control so I can't offer much help with that part. I think there are some vacuum diaphragms that control the center vents, so make sure that is okay.

If your fittings are leaking are they aluminum? It is common for people to get the junky aluminum fittings at the parts store. You should get steel ones. They have sort of a brass looking coating on them. You can get them online and I have seen them sometimes at Pep Boys.

Good luck,