I spoke with my contact at Thule and was informed that for the Sears branded Sport 20-SV cargo box you would need to use hinge # TH14936. My contact also stated that both hinges should be changed at the same time for best performance. I have linked a video review of the hinge for you. But we have recently been told that on that particular box you should use # TH14933 which has a spring with less tension making the box easier to close. Otherwise both hinges are the exact same size and shape.

The original hinges or struts are no longer available for the Thule Adventurer cargo boxes but the current ones, # TH14936, will fit and are what you should be using. There isn't a right and left and the orientation should not matter. It sounds like you might have one # TH14936 and one # TH14933. They are identical on the outside but the TH14936 will have more tension (a heavier internal spring) than the TH14933. You can identify each one when the struts are open. In the lighter one, # TH14933, just below where the smaller arm pivots there will be a black rectangular piece. On the heavier one, # TH14936, that same piece will be white. Both of yours should be white. If either is black then it is the wrong one and you will need to swap it for # TH14936. If both are white and one has more tension than the other then one of them would need to be replaced but I would recommend replacing both because we don't have a way to measure the tension to determine which is the correct one.