I buy old 78s at auction and house sales. There is a good thread on cleaning them but I can't find it.
A cleaning machine is expensive. Some specialists in 78s offer the service for a price.

I use mild dishwashing soap and water and a clean soft cloth. Take your time and do not scrub. Oldhippie's advice, follow the grooves, is good.
Rinse well. Then spray with distilled water from the grocery or drug store. Use a Soft cloth to blot most of the water and let air dry.
I have an old lp brush for final touch-up or for getting dust from 'clean' records.
I found a supply of fresh sleeves, and store the records in them.

When ready to transfer, very lightly spray the cleaned record with distilled water from an atomizing bottle, blotting excess. I turn on the turntable, and with a sable brush, clean dust from the barely damp grooves.

The cartridge should have the right needle, and make sure that the tip is clean and not worn. Use hand lens to examine.

A tip in an old thread says to keep fluids away from the paper label, but a little water can be blotted off. If one concentrates mostly on cleaning the grooved part, very little water gets on the label.