black horizontal streaks on HP ColorLaserJet 5M

I've recently starting getting black horizontal streaks on the front
of output from my HP ColorLaserJet 5M. It appears to be fused, so I
have to assume it is coming from somewhere before the fusing unit as
opposed to after. I've recently refilled the black toner and also
replaced the coating unit (which was 100% used up). IIRC, the problem
started before the coating unit was replaced but perhaps after I
refilled the black toner. The drum is at about 90% used. I have no
real idea how old in time it is because I picked up the unit used.
I've tried the basic cleaning listed in chapter 6 of the manual and it
doesn't seem to have helped. Before I try every cleaning listing in
the manual or on the hp web-site and risk making things worse, does
anyone have any ideas? Should I just try the basic cleaning again?
Thanks.