It's the 'clean' bit of the instruction that's important.
Exposed lead-screws tend to collect swarf and greasy dirt which gum up the half-nut and cause avoidable wear. Any light oil solvent and brush would shift it. Petrol/Gasoline is a good solvent, not recommended because it fumes and is a dangerous fire hazard. Diesel fuel is a shade too thick and sticky to do a good job, and Paraffin aka Kerosene is a good compromise.
When the Super 7 manual was written Paraffin was common as muck in the UK and cheap. It's a practical recommendation. There's nothing special about Paraffin, and WD40 might be preferred today because it also contains a water-repellent. (Otherwise WD-40 is mostly Kerosene.)
White spirit (for cleaning paint brushes) also works well, but make sure any exotic cleaner doesn't damage paintwork or plastics.
How often cleaning is necessary depends on what the lathe is used for. I brushed obvious swarf off my exposed lead-screw as necessary during each session and only cleaned it fully once or twice a year when bored. There are exceptions: I always clean carefully after turning cast-iron, or using abrasives. My preferred method is a stiff tooth-brush and aerosol WD40 because both can get into tight corners but anything that gets muck off the screw will do.
Dave