Threaded comments—Can’t import or export?

I have a large blog with 1,000+ posts and over 15,000 comments. I’m in the process of updating the blog, but I wanted to start with a clean database free of years of accumulated junk.

I’ve been using Brian’s Threaded Comments plugin for years before threaded commenting was part of WordPress. As my entire comments section depends on threading, losing that would be a huge blow.

I have been told that WordPress understands the threading that Brian’s plugin uses, so it’s a snap to convert from the plugin to built-in WordPress threading.

But when I export my blog using the WordPress export tool and import it into a clean database, I lose all threading and cannot figure out how to get it back. I have read in other places in the forum that people have had problems with this, even those who have only used WordPress’s built-in threading rather than a plugin, but no one has answered their questions about this issue.

I hate to think that the setup of my comments system has been lost.

Thanks in advance for your help!