LaserJet 1012 Vertical Fade

Printer works well but has a "slight" faded vertical band about 3 inches
from the left margin, about 1/4 inches wide. New cartridge.
Doing a "half self test" I can see slight fadeing on the drum at that
location.
I surmise this means some issue with the laser mirror or lenses.
Normal cleaning cycle has not helped.
I have the service manual and am tempted to disassemble and gently clean the
lenses [soft cloth/brush] but as this somewhat involved [and I could make
the problem that I can "live with" worse] I thought I should ask if (1) does
my diagnosis sound right and (2) is there is any easier way to accomplish
this cleaning short of complete disassembly.
Thanks for any advice.