hi guys

I have 2 of these Fujinion W f5.6 210mm. The first one I have been using it for a few years and it focused sharp at infinity at f5.6 on the camera ground glass.
However for the 2nd lens (bought a while back but seldom use it), at f5.6, the image will look fuzzy and will only focused sharp at infinity at f16 or smaller. I swapped the lens elements around the 2 lens and narrowed it down to the 2nd lens front element causing the issue.

Anyone know what is the cause and how can it be fixed?

Thank you!