The toilet tank may be 3 or 4 years old. The flapper is Fluidmaster Model 540. Everything is clean and there's no visible tear and wear. But water slowly leaks *unless I push the flapper in the arrow direction* after it shuts (see picture). It can wiggle just by that much (1 or 2 mm) and that's all it needs to stop the leak. I can't think of a way to rotate the flapper by that little. How do I fix it? Thanks.
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