Some users have noted a problem with the Canon engine in both the
LaserWriter and LaserWriter Plus that could lead to trouble without proper
maintenance.
Under the green cover, which hides the fuser roller, are four orange rubber
"fingers" that touch the roller. As toner builds up on these fingers, it
crystallizes and becomes abrasive. This residue then scrapes off the teflon
coating on the roller.
When the teflon coating wears through, toner no longer fuses to the paper at
that position. (The finger on the far right as you face the roller seems to
be affected the most.) The only fix at this point is to completely replace the
fuser assembly, which is a very expensive solution.
You can prevent this from happening by ALWAYS replacing the cleaning felt (the
green plastic strip that comes packed with the toner cartridge) every time the
toner cartridge is replaced.