Looks to me in the second picture, that the bronze
bushing in the top cover is extremely worn to one side.
The relatively close tolerances in the gear
housing and the bushing wear may cause it to tilt on release, and be binding.
It's a gear
reduction unit, to deal with the weight, those gears should be running parallel with no mis alignment.
Look to see if there is and scraping or gouging in the housing, or shiny areas that may indicate a rubbing area.
It maybe machined that way, but looks suspicious to me.
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