those are about 90% easy to replace, the part that goes into the door is a real b*tch to get in properly but it can be done with some long needlenose pliers. you have to take the door cards off, as well as the "chrome" trim piece on the outside of the door and the scrapers. does the window rattle? i noticed that was the symptom when my window runs were getting towards the end of their life...

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1981 NA 300D 310k miles