I'm surprised to read that Vince has had problems with these units. My (plastic) drive seized up and I replaced it with a steel one. The actual changing of one part for another was easy and problem-free. Where I did have a problem was removing the wheel nut in order to remove the seized plastic drive. They seem to do these up rather tight at the factory. Nothing I could think of would loosen this nut, so in the end I cut it off, having bought a stainless replacement first.
Tom