I have a Hauck Duett Twin Pushchair, colour black for one and a half years. It is still in very good condition but one of the parts is broken. The part is found under the toddler seat, red in colour and has a spring in it. Normally this part helps the seat to lie flat or to put it upright. Hauck sent me the part, but i don't know how to replace it.

Baby Gear - Hauck - Duett Twin Pushchair in Black