You may have have to go back and check all the mating surfaces of the turret ring. Sometimes there is a rough patch or a tab slightly hitting a post. Tamiya provides those slip ring stickers but I have gone back and buffed all the turret surfaces before with fine sanding sticks and even polishing compound. Once I even gloss coated my turret ring.
Of course, gluing the slip gear and zip tying the traverse mechanism is my first mod.