I replaced a plastic washer. but It' was not affective.
(It still has tak tak noise but R/A is smoother than before )
I presume the tak tak noise which is can hear after slew for 3~5seconds and disappear comes from the spring or worm and gear.
Perhaps it is the sound made when the gear moves quickly and the force acting on the gear or spring slowly loosens and finds its place.
It's just my idea and I don't know the answer. I will stop tuning any more. In fact, if I put up with the noise for a few seconds after GOTO, there seems to be no problem with tracking and shooting stars.
Thank you for your help!!!