First I'd contact the seller and see if there was 
anything to be done.  SECOND, if it is such a 
dream cel, you're probably not going to sell it, 
and professional restoration (unlike say, if I 
did it) doesn't necessarily destroy the cel 
value, but even if it did, it'd still be more 
beautiful to you. I think a week or two ago there 
was a couple of links posted to a place that does 
professional cel restoration, everything from 
lines to matching paint color and type--and like 
I said, certain types of restoration don't seem 
to decrease the value, only badly done or obvious 
stuff.

If it isn't as much of a dream cel as you made it 
out to be, sell it and cut your losses because 
you already said you look at it 'with regret and 
a sense of betrayal'