my bad i didnt realized that slic3r doesnt give you the option to change solid infill overlaps . Cura and Simplify3d let you change this parameters . but slic3r does give you the option to change you extrusion width for solid infill under print settings / Advanced . you can try reducing the width by 1 or 2 % just to give you an idea .

i didnt play to much with slicer i found cura and simplify3d to be more user friendly.