Welding guns use special copper alloy arms/adapters which function as electrode holders. They attach to the gun on one end and have a cap taper at the other for the electrode. They are frequently called cap adapters.
With time these adapters wear out. A common failure mode is the electrode taper.
The question is can cap adapters be repaired?
A faulty bend or cracked adapter is not repairable.
Tapers are being repaired. This is done on a limited basis depending upon the application, design and condition of the adapter. Keep in mind a repaired adapter is not as strong will not have the life of a new adapter. Repaired adapter could be held in reserve for when new adapters are not available.
A new adapter is the better choice for production line continuity.
Reference: Photo courtesy of -Tuffaloy Resistance Welding Products Catalog