FWIW, I'm going back and doing another thorough pass on English dialogue in Empire (mostly to see if there are any other mono mix differences), and I've actually managed to find a few minor issues in the regular non-mono subs. The biggest one I've found is where Han says a line in a strange ungrammatical fashion, and your brain (or at least mine) tends to automatically correct what he says.

When Leia says "I happen to like nice men", Han actually responds "I'm nice men." The current version of Project Threepio has this as "I'm a nice man." He also says "hydrospanners" instead of "hydrospanner". These are pretty clear when you listen for them.