Just replaced a bad toner cart (cyan) in a CLJ4600. The previous cartridge was leaving a hue over the entire page and had a tendency to drop toner. Now the hue is gone, but color is still off despite calibration. The error log shows numerous Density Sensor Out Of Range errors. My question is, where is/are the 4600's density sensor(s) and can they be cleaned with a brush or similar as in the CLJ4500/4550s? I saw at least one post in HP's discussion forums describing a similar problem; is this a known issue with the 4600? Thanks in advance for any help.