Shacklock Chef door seal?

Need to change the door seal on Shacklock Chef.
Old seal has gone hard and fractured.
How do you get the new seal in?
I've taken the top centre screw out so liner moves a bit but not enough to get new seal in.
Is it possible to slide the whole liner forward?
Any idea where I can get a diagram of the oven showing how to dismantle?
Thanks in advance.