I have a 1985 300TD, it came with the original 2 crossbars on the roof. I just bought a Thule Sonic XL roof box and found that I have to be careful about how much I put in there, because the cross bars will bow down and the clamps of the roof box can end up touching the roof of the car itself. So far so good but I'm worried that a hard bump in the road might cause a dent, or worse, the cross bars will fail. Can anybody tell me the weight that the cross bars can safely support? I wonder if I could just add two more to the car to help support the weight.

If I replace them with Thule cross bars, how much weight can the side rails themselves safely support? Not a big fan of the Thule setup though since the mounting adapters would raise the crossbars up pretty high above the car.

How about the Oris crossbars, which were apparently an original option for the car, since they have a 123 part number and lock in place using Mercedes-style keys? Looks like an interesting option that may support weight better. What are the 5 threaded posts on the top of each bar for?