I hit it with WD40, the a heat gun. Used a screw driver and SMALL hammer to tap the thumb tag. It opened then washed and cleaned which seem to rinse the dirt out of the channels on the little red slider gizzy. Do be careful not to cause a fire with the WD40 and heat gun. It didn’t take too much heat to loosen.
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=== Update (01/15/2022) ===
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I hit it with WD40 and a heat gun. The used a small hammer and screw driver to tap the thumb notch down. It worked fine. Rinsed entre unit and whatever gunk was in the little channels came free. Didn’t take a lot of heat, but the heat did the trick. Don’t set fire to the WD40.
I hit it with WD40, the a heat gun. Used a screw driver and SMALL hammer to tap the thumb tag. It opened then washed and cleaned which seem to rinse the dirt out of the channels on the little red slider gizzy. Do be careful not to cause a fire with the WD40 and heat gun. It didn’t take too much heat to loosen.