If it "looks" like one is already installed, then it is! If you see any kind of lip, or raised edge about .75-1" inside the channel, then it's there! Otherwise, you would only see smooth surface the full length of the channel.
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If it "looks" like one is already installed, then it is! If you see any kind of lip, or raised edge about .75-1" inside the channel, then it's there! Otherwise, you would only see smooth surface the full length of the channel.
I am a big fan of jewelers loupes in such matters.