It’s easy to clean the lens on top of the sled, but somewhat less easy to clean the optical elements under the sled.
To do this, you’ll need to completely remove the sled from the unit and carefully clean accumulated crud from the mirror, the intermediate lens, the diodes, and the pickups, all of which are very tiny and not easy to access.
Fortunately, the lasers in these units are easy to find and cheap and it’s probably more cost and time effective to simply replace it than clean it (though I’m keeping my old sled in case the supply dries up later).
I’ve posted a brief description on how to replace the sled here.