Hi Kieron,
I posted a couple of weeks ago on this thread with the same problem but then, as am still running ML was told to start a new thread as this was for Mavericks. The reason I am responding here again is that after following both threads for the past 2 weeks I see a convergence of a problem first mentioned in March of this year with ML. What I have observed from others: Somehow the print function, whether it is in ML or Mavericks, and whether it is HP inkjet process or as in my case under-IP (wireless HP printer) catches a spooled job and then without notifying us that the job is spooling or still in the queue, begins to eat memory until the machine runs out and has be rebooted. After much investigative work and finally tracking this process down, I have been running Activity Monitor in the doc and periodically I check to see if the process has restarted itself and if so I force quit it, and voila, memory returns.
I repeat I am responding to this here because I have now seen that this is a ML and a Mavericks issue and most probably points to a HP/Apple and possibly OS print software bug. The fact that it started in ML and continues in Mavericks most probably means that it was not given attention in the upgrade. Perhaps now, it will be and fixed for all of us.