I snapped a rear changer cable, it broke in the changer mechanism under the brake hood. Basically to get the remnants of the cable end out I had to take the changer apart. Dismantling it wasn't too bad but getting it back together, especially the spring on top, is proving tricky. I can't tension the spring and the reach of the screw that holds it all together doesn't seem long enough. It's an old part ( possibly 20 years) so is it worth it. Is it actually a servicable part? Has anyone got experience of this?