The decurler is about 2.5 to 3 feet past the fuser in the finisher so it isn't the issue.
The fuser doesn't put toner on the paper, it fuses it, if the fuser had any issue the toner would be on that portion, it just wouldn't stay there (it would rub off when touched).
Have your tech request for a specialist to come in, if that can't be done, go to your sales rep and ask them to do a reversal, the ability to print on 13*19 is clearly stated in the Customer expectation Document on page 6. If your machine can't meet that guaranteed spec (Which is .02 inches from your designed doc) listed at the bottom, you don't have to accept it.
I have recently bought a C70 and the tail end of the printed sheet does not print when I run 13 X19 card stock. My service guy said this is because of the decurler causing the tail end of the sheet to flip up and not allowing the sheet to fuse properly. I never had this problem with my Docucolor 242 (did not have the decurler attachment). Is there a way to fix this problem? I use a .25 inch margin when designing my artwork.