...here's a few pictures of what to look for. This is located just underneath the front of the truck cab. It should be just visible int he box. Probably best to bring a small LED torch to the shop.
This first picture is what to AVOID as it's mis-assembled:
Note the "piston" like sculpted duo. This is misassembled and should be on the inside.
This second picture is what to look for and the one to GET:
Note the two recessed grooves and the blue part sticking outwards.
Remember that part is only about 3cm big.