Exhaust manifold back pressure sensor tube

[Old Driver]

I've got a small air leak coming out between the exhaust manifold and the exhaust back-pressure sensor tube. The stainless steel tube was somewhat melted into the exhaust manifold first time I took it off to clean it. Ive never been able to get the tube tight enough in the manifold to not have air leak out of there. The way I see it I've got four options:

1. Install complete new exhaust manifold.
2. Install used manifold.
3. Drill out the hole and install some sort of threaded insert.
4. Change out only the elbow of the exhaust manifold.

My first option would be to change out only a part of the exhaust manifold with a new part. Wanted some advice if anyone has tried this and if it's difficult. Can the front elbow on the exhaust manifold be removed and replaced without the entire manifold being taken off the head?