the stamping that is not real clear,looks like the NSFK stamp of Icarus,,,,
Stocks of the earlier DLV flyers knife were reissued to the newly founded NSFK but marked with the addition of the NSFK scabbard inspection stamps. So you can find them with both markings.
Should I do anything to preserve the leather?
Personally, I would leave it be. It has survived 70 odd years ok so far. But if you really feel the need to do something a rub over with a museum grade wax, like Renaissance Wax is all that you should do.
Any Guess as to condition level?
condition level is in the eye of the beholder,,,