I have the Star Firestar Plus in 9MM, like you said it’s a very well made Gun, The finish is referred to is Starvel, my book is older but it states to add $30.00 for the Starvel finish.
These guns were made in Eibar Spain, from 1946 to 1972.
There was some junk that came out of Eibar Spain, but that’s not the case with these guns, they hold up real well. My book gives a 100% condition value for your gun at $240.00 but that’s low.
Like I said my Blue book is a few years old, time to get a new one.