First of all, Les, thank you for your expert advice. It appears that the noise I have experienced for a few months was related to a worn out RR wheel bearing which was leaking. Yet I felt the shock throughout the entire car, not just up front. When the hub was rebuilt properly the "clunk" disappeared completely. Also the diff oil had some metal in it so I'll check it in a few hundred miles to see if it is still contaminated. Thus far all seems well. And thanks to all who replied to my previous posts.