Don't know if it's the same but if it's only the
lines you can always resolve the problem with a
correction layer. Studios do this more often that
what we would think. Sometimes is to change the
color of somethign and sometimes to enhance the
lines (or even to remark lines with a more intense
color).

The good thing about correction layers is that you
don't touch the original cel so it doesn't affect
it's original value.

You can take the below cel as an example (Cleo
from Orphen). Notice the well noticeable black
lines. That's a correction layer. In the original
cel the lines are thiner and have faded away a
little in a few points. This correction layer was
made by the studio (at least this is what i
believe) but correction layers can be done by
eanyone with the correct equipment.