Cleaning Up Scans

I just spent around an hour in a futile attempt to clean up one of my cels in Photoshop. I have a couple multi-layer cels that seem to have some sort of "stuff" on them. I'm not sure what this "stuff" is, but it has prevented me from scanning in a few cels in my collection.

When I scan in the cel, it looks like it is covered in dust or something. I'm wondering if there is some sort of magic fix to correct this. Is there some sort of filter or something I can use in Photoshop 7.0 to make this better?

I'm kind of fustrated because I was attempting to use the clone tool to touch up some areas of the cel with less than desirable results. The offending cel can be seen here:

http://cyphr99.rubberslug.com/gallery/inv_info.asp?ItemID=91883

You can see most of the problem areas in the per right corner of the cel and on Natsumi's jacket and shirt...

Thats just dust from the background that has rubbed off on the cel - most of that will clean up if you just wipe the backside of the cel with a cloth. I think you will find that will work a lot better than trying to clean up the scan itself. ;)

I'm going to assume that it's not dust, actually. It looks more like that crud that builds up between layers over time... the stuff that I haven't yet figured out how to clean (and thus why multi-layer cels are the bane of my existence).
I would recommend using the magic wand to select only the areas that are spotty (you'll have to experiment with the sensitivity level setting) and then use a dust and scratches filter on those area only. Once you've filtered a bit (and be aware this will filter out trace lines if your magic wand boundaries aren't quite right) then try going in with the cloning brush. Zoom into about 500% for really good results.
If you still have no luck, you can try pushing the contrast up a bit to lessen the spotting. Also, you can scan at a higher resolution (say, 300 dpi), work on the cel and then downsize it. That'll hide little things you couldn't get.

Yes, the stuff on the cel is some sort of build up that isn't just dust, it is that crud. I tried to clean the cel like Gabriel said but it had no effect...

I'll try what you suggested in Photoshop and see if I have any better results with messing with the image. I think there might be a limit to the amount of good it will do because there is a bubble inbetween the two stuck layers for Natsumi....

There's always a limit. Just remember to save often along the way (as a different file each time) so you can go back to an earlier stage if you're unhappy with the final results. Good luck!