If you have a worn out Rear Differential Mount, I have an easy temporary fix, I used Permatex Ultra Grey Rigid High-Torque RTV Silicone Gasket Maker, I just filled in all the cracks I could find, I left pieces of the original rubber there and just filled in around them. This rtv dries pretty stiff, and so far no clunking. I used up an entire tube, could have probably used a second tube to finish it off, I did it while the part was in the car. I will be removing it and redoing it soon with a liquid polyurethane kit made for motor mounts but will work perfect for this application also, I spoke to the people at Energy Suspension and they wanted me to write up a review and get some feedback. The cheapest I could find the part for is $58

Rear Differential Mount - 1979 to 1983 280ZX :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com