I have had a state electrical inspector red tag panels that had that type of drywaller damage. The panel and wires should have been cleaned with the guts replaced. The drywaller should be back charged for the repair. That what we did to fix that damage.
The inspector's rationale was there was no way to clean off the mud with out causing corrosion to the buss bars and other bolted connections.
BTW after paying for 24 150 amp panels the drywaller made sure his guys did not knock off or remove the panel covers for the rest of that project.
IMO this panel needs the guts removed, cleaned then dried out, and new guts and breakers installed. It would probably be cheaper to replace the panel.
This is about the only time I'll agree with a housing inspector.
