darkzumi
In the original series when the
quintesson fixes Optimus Prime,
there was a metal that protected from the virus that made everyone berserk, as well as heat and some other things.
That was the sentence that I interpreted as the metal was used to fix Optimus. Maybe you need to learn to write because your sentence said there was a metal used while Quintessons were fixing Optimus Prime that protected him from the virus. It's either called a misplace modifier or subject noun agreement. In any case "a metal" isn't a coating. The coating could be metallic (ie liquid alloy). If you try to fix a car using a coating, most likely it will not run. You can detail a car with a coating.
Just saying, but hey interpretation in writing can always be mistaken. But don't claim others can't read unless you are absolutely certain what you write is clear.