In article , Adrian
writes

Thought he had a "proper" LJ5? The 5P was very different - much smaller.

Thanks for looking out. Jim said in his OP:

My folks have a Laserjet 5P that will only print if fed single sheets
one at a time through the "other media" (sic) flap. I.e. if it takes
paper from the cassette underneath it will jam, but if fed manually
single sheets all is well, if infuriating!

so I think I have the right printer.

--
Mike Tomlinson