Still using the one that come with my S5 here and it's still fine and i have 108 days of run time on the printer. It's likely you are using prime blobs at the start and you get left with a bit of filament on the cover around the nozzle due to how the prime blob works. So without seeing any image i would say its just burnt filament what you can just clean off.
How fast it will degrade depends on the material and temperature used, but it should last for more than just a few prints normally. Luckily the part is super cheap (like 1 euro) so in case of doubt just replace it. It’s a part of which you always want to keep a few on stock
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