You have a very rare M1911.
According to Clawson's book "Colt .45 Service Pistol" your pistol is in the second batch of M1911's that the Navy bought in 1912. He notes that they were Colt USN (Naval Militia), so maybe the second lot did not go on ships. Another book says this serial number range went to Brooklyn Naval Yard.
The pictures in the book are black and white and I don't know what the original finish should have been, but the other book shows an early Navy with a blue finish.
I am not a holster expert. If the holster is an original WW1 or earlier holster just set it aside. If it has dry rot there is nothing you can add or do that will make it last longer other than stop handling it.
If I'm not shooting, I'm reloading.