Thanks for your sugggestions John. That is the site where I got the driver after talking with Applecare, but resetting the printing system with the option - key, along with some settings experimentation, seems to have done the trick! Prior to posting here I spoke at length with 2 different people at Applecare as well as HP, but they couldn't resolve it.
If anyone else has this great old workhouse of a printer (1999, no USB but has Ethernet) here's what worked for me:
Download the latest HP driver from the apple website John mentions. Reset the printing system with the option - key. The LaserJet 4050 doesn't appear in the Nearby Printers list. However I added it through its IP address (you can get this by printing out a Configuration Page from the printer's internal menu). Go to Preferences, select Print/Scan, and click on the IPP pane. Enter the printer's IP, set Protocol to HP Jetdirect-Socket and Use to HP LaserJet 4050 Series. The printer will set up. however in the Print Window dropdown (below Copies & Pages) "Unsupported PDE" appears and I get a low toner message (not true).