Need help identifing a Russell Green River Works 4215 I found.

I was at a friend's shop and she had these two knives she wanted sell, since any kind of weapon makes her unsettled. So I took them off her hands. The one I want to see if you can help me with is marked, "Russell, Green River Works, Made in U.S.A., 4215" and has a very nice carved antler handle on it. On the end of the handle has a bear craved on all fours. I will attach some photos so you can see it. Any help would be appreciated and also the blade has some rust spots on it. What would be the best way that I can clean it and protect it? Please advise and you can email me directly at Thanks so much for any help you can offer.