Using Loctite ( it should be the blue one ) would not hurt anything so go ahead and use it . One possibly is the treads on the steering tube , are they ok or are they a little mess up do to the key washer or in this case the cable hanger . If this is the problem using a tread chaser (file ) will clean them up . If the treads are off a little they can keep the locknut from tightening all the way . Another trick is use another spacer with the cable hanger .