The cords are broken on my window counterbalances. I've taken one out and find it is pretty well sealed with pins not fasteners. I pried the top off one and find a clockspring balance. I think I will be able to replace the cord on this one, since I could get the spring end back into the slot withou removing from the housing, but i may not be so lucky when I take out others. First is this some soecial cord or can I use anything I find that is similar? Second told by the mfg. (Pella) this style is no longer available and no suggestions where to find a substitute. Is there any place that specializes in window counterbalance replacments?