There is very little in the Marvel Universe that Captain America values more than his trusty shield. However, this vibranium/adamantium alloy was nearly lost forever at one point in the late '90s. But in an unlikely turn of events, Steve Rogers was able to recover his shield, thanks to one of Black Panther's greatest villains.
In 1998's Captain America #2, by Mark Waid, Ron Garney, Bob Wiacek and Joe Rosas, the Sentinel of Liberty lost his shield at the bottom of the ocean. Eventually, the shield was recovered, but when it was dropped on the floor, it shattered upon impact. This was a shocking turn of events, considering the indestructible nature of this vibranium/adamantium alloy. After the Avenger replaced it with an energy shield for a year, 1999's Captain America #21, by Mark Waid, Andy Kubert, Jesse Delperdang and Gregory Wright, revealed the truth behind the shield's destruction and paved an unlikely path to its restoration.
Years before, in Secret Wars #12, by Jim Shooter and Mike Zeck, Captain America's shield had been destroyed by Doctor Doom. Thanks to the all-powerful Beyonder, however, Steve was able to will his shield back to its original form. Still, one tiny molecule was restored out of its original alignment. Since vibranium converts sound and energy into power, each time the shield was hit, this odd molecule spread. This "vibranium cancer" infected neighboring molecules in the shield, eventually destroying it. Even worse, the cancer spread to other sources of vibranium, leading to dangerous explosions.
The power of the vibranium cancer grew as it spread, ultimately reaching the most dangerous source of the rare metal: Wakanda's vibranium mound. If the cancer traveled to the mound, there would be an eruption surpassing nuclear levels. In order to nullify the vibranium mound's eruption, Tony Stark created a transformer that would intercept the mound's frequency. The transformer would then alter the mound's frequency so that the cancer wouldn't reach this mass-quantity of vibranium.
Of course, the transformer would need to use Captain America's shield to perform its task, destroying the shield in the process. The Star-Spangled Avenger reluctantly took his shield to Wakanda where he was attacked by a horde of pink constructs resembling a stampede. After dispatching these constructs, Steve found their creator: Klaw, Master of Sound.
Klaw wanted to eradicate vibranium, as it was his only weakness. In the ensuing struggle, Klaw destroyed the transformer. Additionally, Klaw absorbed the shockwaves of the erupting vibranium mound and attacked Captain America with full force. Steve desperately raised his shield to defend himself. Suddenly, The Sentinel of Liberty saw that his shield had been restored to its full form.
When Klaw absorbed the waves emanating from the vibranium mound, he essentially did the transformer's job and stopped the cancer from spreading. Furthermore, by hitting Steve's shield, Klaw inadvertently realigned the shield's vibranium molecules, repairing it fully. With his shield restored, Captain America was able to easily defeat Klaw. One noteworthy aspect of this story is how it essentially serves as a follow-up to crossover event Secret Wars. For one thing, there are serious consequences to Captain America restoring his damaged shield. The Beyonder's energy wasn't quite perfect in repairing the shield, illustrating some major complications to this seemingly magical fix.
Klaw is also an important part of both Secret Wars and its spiritual successor here. In Secret Wars, Klaw served as a vessel for the Beyonder after Doom had seemingly killed him and stolen his power. Klaw unsuspectingly saved the day by hiding the Beyonder until the Beyonder emerged to defeat Doom.
Similarly, this story saw Klaw unknowingly save the world by absorbing the shockwaves of the vibranium cancer and preventing the vibranium mound from exploding. Moreover, Klaw restored Captain America's shield to its rightful form. He may be a villain, but Klaw helped Steve Rogers when he needed it the most.