Why does it fail right there? It appears that because of the bend the rust prevention coating is compromised at the factory. It just takes time and simple humidity in the air is enough for rust to form and work under the coating and grow.
Every E53 I guarantee has this problem. A simple prevention would be too scrub with steel brush and hit with some naval jelly then Rust-Oleum paint. If done closer to 100,000 miles 160,000 km, you will prevent the failure. That would be a good time to repair the siphon jet pump o-ring.
I will be checking my wife's e53 asap. I'm going to just drill a 2-3" observation hole to get into that space without removing the whole panel. I should be able to prevent hers from failing like mine did.
If hers is "made of rust" as mine was I'll splice in a piece like mentioned above it will save about 4% hours not replacing the whole pipe.
update: my
amazon review is live. It includes a 12 minute video showing exactly how to fix the defective tool and properly make a perfect iso bubble flare every time.