Weird Xerox C1618 Behaviour

I've inherited a 3 year old C1618 from an acquaintance. Everything works okay except for this weird behaviour.

The first few centimeters (about 4cm, same length everytime) of every fresh piece of paper is very faint (barely visible). After that, everything is normal. If I set it on duplex or manually refeed the same sheet of paper, the printout will be normal. This is totally repeatable and happens to every single sheet of paper I've printed so far.

The person who I got the printer from said he never had such a problem and the printer's been rock solid the past three years.

I suspect damp paper, but another laser printer I have that uses the same stack of paper has no such problem.

Could something have broken during transit?