I've been thinking about this for a long time, 
and I've wondered:

 For those out there with cels with significant 
line loss/fading create a new line layer from 
their sketch (assuming they have one)? I know 
that animators used a special carbon machine 
xerox thing to make the transfer.. but I'm 
wondering if this is a possible solution to the 
line fading problem? 

Don't shoot me if this is just an insanely stupid 
idea ^^;;; Just curious...

~Tara