Here's a few pictures I took as I pulled the printer apart.
Gearing clogged up with ink - flow appears to have come from left and spread thru the gear cogs. For how long, no idea.
Star wheel motor assembly clogged with ink. Far left gear cog is missing with stud snapped off. Not that I noticed it until later with a closer inspection.
Printer opened up: even ink is running down the leg. This end is up against the wall so I never noticed it. I'd like to think the syrupy ink caused the failure, not a symptom of something else. This was one of the first Z3100s, I've had it for 4 years.
Solving the ink spillage may just be giving everything a clean. A replacement motor assembly is on order - my supplier didn't have any on stock- mine is the first failure apparently in NZ. Seeing as this is used in more models I was disappointed about the lack of stock - they'll be keeping more in future, but I'm off line for about 2-3 weeks. Luckily my rep happened to be up my way and looked at what happened, with photos sent back. They may send them to HP but who knows.