LJ5 doesn't have the intermittent jamming issues that the 4 series had. It is my understanding that the 5-series fuser runs at a slightly lower temp which lessens the amount of paper curl and thereby less paper path issues. Both the LJ4 and LJ5 are built to last forever with maintenance so a rebuilt or re-manufactured printer is fine. All they typically do is a roller kit, or if the pages count is high, a fuser kit in addition and it will be as good as new.
What you get for a more modern printer is that they are much faster but they are not built to last nearly as long. If you want to buy modern, start out looking at the monthly duty cycle as the primary statistic to pay attention to.
Avoid anything that is GDI (host based printing)! At some point, that printer will have printer driver issues because the manufacturer won't update their driver to a new OS and you'll be left with a doorstop when you move to the new OS.