I had the same problem last month, same window too. I see that you have already taken out the regulator assembly and see that one or both of the cables have slipped out of the blue plastic. The updated replacment regulators you get now have a strong metal housing around where the cables hook in. The rivets from MB are really strong brass ones (about 20 cents each) and they require a great deal of force to pop. I had some aluminum ones the same size, so I used 2 brass ones and 3 aluminum (couldn't squeeze any more) and no problems.
hope that helps