Keepitup
Possibly this is not about the TCDS, but probably about modifications and / or repairs installed on a 30 year old helicopter (or older) under CAA / EASA regs.
But whatever you do.....DO NOT deregister the helicopter until you have that piece of paperwork, the pain would then start.
Might be easier to contact your local FAA DER, who may sort out a different route for export, the CAA were B.......S to me some years ago so had to use that route with an AS355F1.