Like some before have said, if it used to slide freely and now it
doesn't, it's most likely dirty.Â* The first logical step is simply to
clean it.

On 2/18/2020 8:28 AM, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
I have often used an old candle to rub wax onto sticky sliding/meshing parts (drawers, zippers, etc). Should work here too.

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Dan, 5J