Ricoh photocopier copy issue

Hello, I just got an old Ricoh photocopier, it was working very well but there were large black streaks appearing across the copy. So I took apart the mirrors to clean them, as they were indeed covered with a thick layer of dust. After reassembling, I tested it and there were no more black streaks, but now there’s a new problem: the copy is shifted. I’m not really sure how to explain it, it’s like the print is doubled with a 5 millimeter shift downwards, a bit like a watermark of the copy in question with a delay. If someone could tell me what this is coming from, or at least give me a lead.

Thanks in advance.
Best regards.

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