Hi there,
I know that a professional cel restorer can fix 
the line fading with no problem.  But, you have 
to send it to them usually.  

Boy, I need to be a spokeswoman for this place:  
try calling Fine Toon Art Gallery in Houston, 
Tx.  They send all their cels and art that need 
fixing up to a woman in California who used to be 
an animator at Disney.  She fixes all kinds of 
problems, as Im sure line fading is a VERY common 
issue with cels.  I hear she is also quite 
reasonable with pricing.  Here is the URL for 
Fine Toon though.  It may be a lot of trouble, 
but if you love the cel enough to get it done, 
then I bet they'd do a good job for ya:


http://www.finetoon.com/cgi-bin/finetoon/

I need to have a couple things fixed up 
myself :).  Line fading badddd.  I dont have any 
cels yet that have it very bad, but I just bought 
one that I think has it, so I might be sending it 
off for a "toon-up", haha!