Ummm....
.... yeah.
Sorry, but tweaking and recompiling my macports boost to support OSX 10.5, which is not longer being supported by Apple (or Chrome or several other popular projects) just isn't very high on my TODO list.
Figuring out why it used to work is even lower on my list.
Perhaps you can convince people that you're trustworthy, and release a 10.5-compiled binary yourself.