i did my front window not so long back rear is same sort of assembly.
take assembly out buy a bycicle brake cable grind the big crimp on the end down to size, cut the cable at the right length (might take a few goes had to make 2 for mine cos made first one too short Doh!). now the tricky part a pillar drill is most helpful. take a 6 inch nail cut about half inch off drill an approx 2mm hole down the middle ( make sure you got loads of drill bits they have a habit of snapping), cut to correct length, put on end of cable, with cable threaded through outers, crimp on with hammer, apply a little spot of weld to the end to make absolutely sure its tight on there. grind to fit hole in motor pulley. refit assembly and glass. bobs your uncle fannys your aunt. hope that helps