If you were able to take the lens assembly apart, it means the epoxy seal of the sensor housing has been broken at some point. If so, it's not likely you can correct the blur. Focus might help, but there are two kinds of lens assemblies. One can be focused, the other can not. If there is an obvious threaded joint in the middle of the lens barrel, the epoxy can be cut away at that joint, the camera refocused, and the joint can be resealed. If the interior surfaces are already contaminated or damaged, focus is not going to help. A new lens assembly will be required.
Has the camera ever produced a clear image?