I have a 1988 560 SEL that's in reasonably good shape, but in the last two weeks, the moonroof has started to make a scraping sound when I open it, and it doesn't open/close as fast as it used to. I used WD-40 to lube the rails, which in hindsight, probably wasn't a good idea, but it helped a bit, but the opening and closing is still slow. Does the moonroof have rollers that can break off, or is it possible that's it just dirty?