Kohler K7030

Any experience with re installing the "barrel seats"
A old shower stem

I assume you are referring to the ones that are similar to the American Standard ReNu barrels. If so, as long as you have the metal washers in the correct locations and tighten it snugly, there should be no problem. If you mean the "newer" Valvet stems, then you have to use the stem to prevent twisting while tightening the cap.