Try some silicone spray. Also make sure the scrolls and grooves that the tambor sits in do not have any obstructions. It is easy for something to get jammed in the scroll area that will cause problems. Most of the time, the silicone spray will smooth things up so the tambor will move again. Tambor is very expensive to replace.
I had a screw head sticking up on my kitchen cabinet rail that kept the door from operating properly. Try a mirror and a flashlight and see if you can see something in the way.
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