The comic titled "Junkheap Hero" can be found inside of Star Wars Tales #6.
While casually strolling along the streets of a Tatooine city, C-3PO and R2-D2 discuss the dangers of their current location and time. Specifically, they note that they are dangerously close to the "The Empire's" domain, and that a "Thriving black market on robot parts" is active.
In a nearby Imperial headquarters, Darth Vader is in consultation with a group of Imperial officers regarding the situation on Tatooine. Vader expresses his dissatisfaction with the officers' slow progress in planting a spy within the Rebel's ranks to locate their hidden base. To rectify this, Darth Vader instructs them to dispatch a squadron to capture one of the "Two Droids, known and trusted among the Rebels" (namely, R2-D2 or C-3PO.) Vader believes that the Rebels would be less suspicious of a mechanical spy, making a reprogrammed droid an ideal means of relaying plans directly to the Empire. Vader emphasizes that the officers' lives are contingent upon the success of this plan.
As C-3PO and R2-D2 continue their walk through the city, two Imperial officers seize R2, stuffing him into a sack and whisking him away unnoticed. After a few moments, C-3PO realizes that R2 has been abducted and rushes back to Luke Skywalker, shouting. Luke, deciding that a solo rescue mission would be faster, tells the droid that he will meet him at the Core building.
Upon arriving at the Empire's Core Building, Luke observes the officers and a mechanic examining R2 through a window. Luke suspects that they are about to tamper with R2's memory. Acting swiftly, Luke spots a junkyard adjacent to the building and conceives a plan to deceive the officers. He quickly assembles a convincing replica of R2 using the discarded parts.
Luke then plants a small explosive device on a wall of the building to create a diversion. While the officers are distracted by the explosion, Luke sneaks through a window and swaps the real R2 with the junk replica. He then escapes with R2 on his miniature speeder. Luke and R2 embark on a mission that lasts for several months, without informing C-3PO of their whereabouts. Luke assumes that Threepio will "figure it out once he realizes you're not around."
The officers return to the office to find the R2 unit falling apart. In a panic to eliminate the evidence and avoid Vader's wrath, they toss the R2 replica out of the window and into the junkyard below. C-3PO, who has finally arrived, witnesses R2 being thrown from the window and cries out in horror at the sight of his friend's dismembered state. Threepio, perched atop the mountain of junk, vows to rebuild his friend, even if it takes months to do so.
Bender, the famous character from Futurama, makes a cameo appearance as one of the discarded droids towards the end of the story.
In an error, C-3PO incorrectly refers to some Imperial officers as agents working for the "Trade Federation."