how to access the rear tow hook of the Dapol 0 gauge class 57xx Pannier.

[RvSwol]

Hello Forum Members,
Is there anyone who can help me how to access the rear tow hook of the Dapol 0 gauge class 57xx Pannier.
The tensile stress on the couplers in the curves with a radius of 1033 mm is too high that these couplers break, or the Dapol autocoach derails . It looks like the rear hook is stuck. 
The hook at the front of the Pannier has much more freedom of movement and there the problem does not occur. 
The supplied drawing of Dapol only provides information on the installation of a DCC decoder. 
I do not live in the UK, so going to Hattons or Osborne models is a big undertaking given the European customs formalities. 
Thanks in advance for thinking along. 

Rupert.