When I received a dead unibody 13-inch 2010 from a friend who used that laptop harder than any laptop I’ve ever seen or known, the innards were beyond filthy, and very likely the CPU and/or controller burnt themselves out after the fan and vents were thick-caked with gobs of dust (there are pictures, and it would blow some minds on here).
I decided to give it my best go and I completely disassembled, then cleaned everything inside, including the dismantling of the SuperDrive. (The MBP didn’t come back to life, and it was unresponsive to a MagSafe adapter or a charged battery connected.)
When I opened the SuperDrive, there was, surprisingly, only a couple of little dust bits on the lens (and a few other dust bunnies elsewhere in the case, away from moving parts), but it also had this very fine film which made the lens glass a bit cloudy (pretty sure there was some toking in its proximity during its lifetime). I gently used a lens cloth to clean it, and it returned to how one would expect it to look. Does it work? I have no idea. I haven’t tested that drive, though I suppose I ought to.
All of this to say: sometimes it isn’t the dust flecks which get the lens of an optical drive, but the finer, cumulative particulates (including local air pollution) which make lenses unhappy. I’ve seen similar clouding in portable CD player lenses, as well.
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