Well, its high carbon steel, with leather, and not off the shelf mfg. and it was hidden for a reason...So somebody thought very highly of this blade at one time...It could be a bonafide murderous blade? Who knows?...
So yeah I'd take the time and restore it somewhat...I'd also practice throwing it on 1, 1/2, and 2 rotations, pulling it out of my boot or waistband effortless and smooth...It looks good and balanced and was somebodies precious at one time...That blade was built not intended to cut bread or cucumbers...thats a Man killer blade...
I'd clean it up and get to know it a little...It will speak to you as to its history if you spend some time with it and listen....
Its a light fast underhanded thrusting blade...or a chicken or cheese chopper...Who the hell knows when it comes to what knives have seen? not many of them get hidden on top of the duct work for no reason though is all I'm saying....It could be a Hatori Hanso?....
I'd buy it from you, or at least offer you something, but I'm pretty well set in the bladed and murdery knife department...Which is what that blade is, or a turkey carver or a cheese cutter..so yeah..I'll offer you a dollar and a Merc dime and pay shipping for that blade..