Early Takumars were uninspiring, though there were isolated shining stars that are still sought out today. The modern Pentax SMC optics are worlds away from Takumars, though oddities of optical pedigree do exist e.g. Distogon, Biogon heritage designs to account for the limited mirror box real estate.

Dirt making its way into the focusing barrel can be the cause of the scratchy focus. I have handled a Takumar 105mm with this problem very recently.

But if it is labelled Korea, it is certainly not a Takumar: the lenses have always been of Japanese origin.