Underwood 1915? Standard Portable Typewriter in Green Faux Bois: Have questions!

I am SO EXCITED!!! Just bought this from my cleaning lady's son for $40! Have always wanted an Underwood but never ran across one I could afford. Here are my unsolved mysteries: Patent says 1915, but how do I tell what year it was actually made? And, here's the big question: The clip that holds the spring that sends the bar back when it reaches the end is broken. How and where do I find a part to replace it with without Jerry rigging it? And, yes, I can say Jerry rigging. I'm entirely of extremely recent German heritage. Lol.