A slight amount of rotational play in a mounted lens is generally normal. Most bayonet lens mounts have a tiny bit of movement because of normal manufacturing tolerances. If the lens clicks in, stays locked securely, and the camera functions properly, a very small back-and-forth movement like you describe is usually not a defect.

What would be more concerning is excessive looseness, wobble, poor locking, intermittent camera/lens communication, or changes in image alignment. But based on your description, this sounds like typical bayonet mount behavior rather than something that needs repair.