Hi!

Good luck finding the part.

I have at least one DeskJet 5850 that's only good as a locally connected
printer after a firmware upgrade that went wrong. Apparently the internal
J6077a JetDirect isn't actually upgradeable or the firmware is bad. Either
way, HP has never commented, doesn't sell the (removable once you get the
printer apart) JetDirect module, or offered to fix this problem.

If you can't find a replacement gear, you might try making and installing a
new tooth. There's information in the FAQ about doing this.

William