One who obtains a patented device from a legitimate source is permitted to repair that device, or replace a broken or exhausted part, without further obligation to the patent owner. See Husky Injection Molding Sys. Ltd. v. R & D Tool & Engineering Co. 291 F.3d at 785-86 (Fed. cir. 2002). On the other hand, one cannot reconstruct the patented device to such an extent that one is, in effect, building a new and unlicensed device. See Aro Mfg. Co. v. Convertible Top Replacement Co., 365 U.S. 336, 346 (1961). The line between repair and reconstruction is a difficult one to draw. In fact, although it defies logic, one may be allowed to replace an entire device over a period of time by the successive replacement of worn out or spent parts, as long as in no single instance are the replacements so extensive that they amount to a reconstruction.