I had 2 earlier this year that needed the firing pin mod. Winchester is still supplying the parts. I made the change myself, there are a couple of videos on Utube that I watched before digging in.
You have send in the old parts with the serial number and Winy will send the new parts. I had to contact them twice to get the $30 dollar check"s" (one for each gun) to cover the "gunsmithing charge".
I still have one in 308 it is a pre64.
