the clips are on the inside. heres a picture of what they should look like. ive seen em so rusty that they look like they are not even there. use a fine punch, or flat blade screwdriver to knock them out. rap a few times on the end of the cap you're going for first. that should make it possible to knock that clip off. repeat as necessary.
J ust
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P ocket
J ust
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P ocket