First, I don't know. But I do service Nikon film scanners, and in large
volume over a period of years. On Nikon scanners, while dirt and dust
and cleaning are HUGE issues, the problem is usually confined to one
single item, the "lower front mirror" (the overall optical design of the
last six Nikon scanners .... LS-2000, 4000, 5000, 30, 40 and 50 are all
substantially the same). But how accessible the relevant surfaces of
the FS4000US are, I just cannot say. One thing I can tell you ... I
also service laptops ... and if either these scanners are laptops are
disassembled by untrained users ... they often do enormous damage.
However, for the Nikon scanners, there are some online instructions
(with photos) that reduce the risk.