Another 70's owner here. Couple of suggestions...you can buy replacement parts, or you can upgrade. I am upgrading my vents to a Fantastic Vent
over the front living area, then adding a semi recessed Thin Line
fluorescent fixture. Center vent is staying stock, but getting the old automotive style bulbs replaced with fluorescents. (it takes some modifications) The rear vent over the bath area is being replaced with a Maxx Fan
. I have most of the bits and pieces but haven't had the time to "git er done"