Also, when you can't reach the labels that came off the sheets and adhered themselves inside your printer (thankfully in the exit rollers after the fuser), run some blank sheets of plain paper through. They'll jam up alright, but if you pull them out carefully, they'll bring the lost sticky labels with them. It may take a few sheets, but you will eventually get them all.
Thankfully the HP LaserJet 5n is a tough machine. And that, if you're wondering, kind of summs up the first half of my day. The rest got better.