Hmmm... I think you have a completely different 
problem from what Blueheaven described. I think 
your problem is that you can't get rid of the 
water looking spots between the two layers, even 
though your layers are flatly pressed together, 
is that right? I have encountered this problem 
before with one of my multiple layered cels. It's 
a pain I know, because you clean it and dry it, 
they just won't go away. 

Well, since you are open to all suggestions, I am 
going to tell you how I got rid of this problem. 
It sounds really primitive, and all the other cel 
collectors will probably laugh at me, but I 
wanted to help you, because I know how frustrated 
I was when I had the problem. 

Here we go! Take some corn starch or flour and 
apply a thin layer of it between the cel layers 
where water spot will appear (Use your fingers to 
smear it around a little bit). Keep the cel flat 
on the table, and keep the layers separated. Let 
it set for a couple of minutes, and GENTLY brush 
the flour off with cotton cloth so none are still 
visible. Close the layers and the spots should be 
gone. What you really did is made the inner 
layers smoother, instead of so clean it's 
stactically charged and obsorbent.

I know it's primitive, and you are probably 
thinking "Is this guy nuts, I'm not putting that 
crap on my cel." Hehe, understandable! Well, it's 
up to you. Hopefully, you find a way to get rid 
of them different from mine! Good luck!