I don't personally find the presence of a 
corrective layer to be an issue. Mistakes happen, 
and I find it fascinating to see how the problems 
were worked around!  Of course, your mileage may 
very; I know some people are much more particular 
about the cels they purchase than I am, and would 
consider a corrective layer like this -- even if 
it was made by the animators themselves and was 
used in the show itself -- to be a major flaw.

One of my cels has a corrective layer -- the 
painters filled in an eye highlight on accident, 
so an overlay was made to correct the problem.  
You can see the scans of the various layers by 
clicking the link up above.  Looking at the cel, 
most people would never know there was another 
layer there.  The only thing that gives it away is 
that the lines in the hair on the bottom layer 
have faded slightly over time, making the lines on 
the corrective layer stand out a bit more.  When 
this cel was new, it would have blended perfectly.

It's too bad the paint chipped when you separated 
the layers -- if it's that chip that's bothering 
you, then I would just fill it in and to hell with 
value! You bought the cel because you loved the 
image (I assume) -- does the presence of the 
extras layer/paint chip really change it that 
substantially?

Just playing devil's advocate.  ^_^

__
The Lizzard