Does it still work OK?
Feel the subwoofer - are there strange patches?
Are you sure it came from the subwoofer?
It may have been there before, or something may have been spilt there.
I'd say if it's not playing up and the substance doesn't cause problems, leave it be - I have no idea what it could be or what could have caused it to start leaking.
I must say, this is a bit different from the usual questions
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