I have seen a few older post about this issue, but wanted to see if there was any new input on how to fix this issue. I grouped multiple objects and although they appear to line up properly they leave lines when they merged. I understand that if I have a bit of overlap the lines don't occur, but it was not possible with the objects I had and my skill level... I also understand they will probably not affect the print, but it does effect the cleanliness of the rendered preview images, make the object look unclean.
Merged Lines after Grouping