Chosen Solution
My magic mouse’s left click has suddenly become very difficult to click. It no longer makes the click sound, and the resistance when pushed has gone out. If I open this thing up, what do I look for to fix it?
From what you are describing, I think that the silver spring seen in this picture may be the culprit. Check out the iFixit teardown to decide if you want to tackle this. You might be able to buy one cheap on eBay for parts.
You could simply replace the button. Her number D2FC-7-H on AliExp.
