Welcome aboard! The rear window deal...
sounds just like mine, I haven't fixed it yet but took the door panel off and the window track sliders were off track and broken. You need to pick up a couple of the slider clips and replace the old ones and you should be good to go. When you get them get a few extras so you dont have to travel back when you have a problem with any others. It could be the regulator but it sounds more like a track issue to me. You could pull the door panel and look first of course, dont pry on it hard the door panel is tricky to get off, pull, lift etc etc.
Jeff
95 E34 530I V2.37
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Those who make peaceful revolution impossible will make violent revolution inevitable.
John F. Kennedy