Near the end of Civil War,
Tony destroys the majority of Bucky's metal arm in a fight.
The post credits scene shows the extent of the damage.
The Winter Soldier has been operating for decades, therefore the technology to build his arm has clearly been around for a while.
However, seeing as the majority of HYDRA's operations have been taken down at this point, anyone with the knowledge of it's original construction would likely be unavailable.
It would probably be quite easy to
build Bucky a new arm from scratch
using Stark tech or something similar. However, unless it can be reverse engineered it appears to be quite unique among anything that we see within the scope of the MCU in the modern day.
My question is: Is there anyone alive who has the ability to restore it to its original design, so that it would be identical to before?