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Recommend you just replace the ceiling liner for now, as it wont cost so much and will make a big difference to the feel of the interior. Any reputable upholstery shop should be able to do it. Of course make sure that the leak that originally caused the staining is fixed first! Throw in a new set of floormats and go over all the surfaces with some cleaner followed by armor all and and I think you'll be surprised how nice the interior will look.