Hard drives are rarely repaired. We can reforrmat such but can you reveal it's damage?
The Mac Pro pc was made using a modular construction. This will make adding a PCI Express (Peripheral Component Interconnect Express) card a simple affair that could be accomplished within 10 minutes. You may need a single tool--a Phillips jeweler's screwdriver--but no special skills or expertise in working with computers. Installing the PCI Express card does not violate any warranties about the Mac Pro.
But how to repair a hard drive with an external enclosure?