I've tried the detergent (use very sparingly) in luke-warm water and it works well, getting rid of all sorts of gunge.
Use a soft brush (like a very soft toothbrush or nailbrush) to go round the grooves, then flush the record thoroughly under running water (it helps if you've got soft water).
Dry the records flat with towelling above and below, and then - with your best and sharpest needle in the player - transfer them immediately to MiniDisc or CD.

PS: My parents' state-of-the art radiogram had settings for 78, 45 and 33rpm, but also for 16 rpm (which made 78s sound veeeeery straaaange indeeed). Was that used for voice recordings or what?