Help Needed: Motorized head mechanism squeaking and catching at 45 degrees

I added a 12V high-torque DC wiper motor to rotate my Skelly's skull left and right with an Arduino microcontroller.

It ran fine for the first 3 days on the workbench, but now that it's mounted inside the neck column, every time it turns past 45 degrees to the left it makes a sharp plastic squeak and stutters.

• Motor: 12V 45 RPM wiper motor with nylon gearbox
• Neck joint: 3-inch PVC coupler on lazy susan bearing ring
• Power: 12V 5A regulated power brick

Could this be thermal expansion on the PVC collar, or does the lazy susan bearing need dry PTFE lube instead of standard grease? Anyone ran into this issue?