Chosen Solution

I’m not sure why this would happen. I don’t know if i was just irresponsible or if it just happened but my L button is no longer working. Would it be gunk? All the other buttons still work. Should I get a used joycon if I can?

Yes is sound like you got something sticky under there. I don’t really know any way to get it out. Purchasing a used Joy-Con is definitely an option.