Mold lines, which are also referred to as weld lines, occur during the normal manufacturing process of the iBook's plastic top case. The lines occur where molten plastic comes together within the mold. On the iBook, these lines are faintly visible on the top case above the keyboard.
These mold lines are normal and no repair of the iBook is necessary.
Figure 1 Mold lines
Because the mold lines are very faint, the locations where they may occur have been highlighted in red in Figure 1.