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12 hours agoIf it were me I would break it down to the same level you had before to clean it and try it anywhere and everywhere you can think of as you re assemble. Look for parts that look similar to the ones it is next to on the drawing, long shafts it can slide onto, or little (probably dirty or worn) niches or nubbins that the spring could tuck into or onto. If I had to guess it is probably a spring for bump feeding more string, but it’s just a guess.
Good luck!
It looks like it could be it to me. Seems like a weird spot for a spring lol probably why it’s not intuitive to reassemble.