The roof on my W208 doesn't retract unless I 'hold up' the front portion so that it can bend. And when closing it now bangs against the header rail rather than holding off a few cm's. I looked under the internal lining and found a steel cable adrift, the cable has parted company with the fixing at one end and is frayed, I think from looking at an exploded diagram that this is the 'balance cable'? Putting two and two together this appears to be the problem but my question is how difficult is this part to replace? If I can buy the part is it a simple job to replace?