Hello Derek, I am an HP Support Engineer. I am speaking for myself and not for HP but I believe that I can assist you.
The LaserJet 4100 series firmware wasn't flashable; to update the firmware required replacing a DIMM installed on the formatter. I don't subscribe to the original forum this was posted to so I am adding my response here. The symptomatic behavior you describe sounds like "page spew".
What driver and version are you using and what is the OS?