Update y-corners.scad

 // Bottom hole
  translate([0,11,10-1]) rotate([0,90,0]) translate([0,0,-5]) cylinder(h = 270, r=5.4, $fn=30);
  // Top hole
  translate([0,11,30+1]) rotate([0,90,0]) translate([0,0,-5]) cylinder(h = 270, r=5.4, $fn=30);

Removed the -1 from the 10 and 30 for the holes to match the motor mount.