Distressedgfof280zxowner

My boyfriend owns and 81 280zx turbo automatic with an R200 differential and half shaft axles. At the moment the car is having an issue of a clunking noise in the rear end whenever we let off the gas and the rear end jumping to its own direction. Both do not happen constantly. You can also hear a grinding noise and whining constantly. I have looked everywhere and can’t find a new diff or even a whole new rear end. I have already spent over 2000 on this car trying to make it run right and am trying to prevent him from scrapping it. Any suggestions please?!