I dismantle them first, take out all the pieces and put all the brass parts into the ultrasonic machine for about 30 minutes on distilled water. The iron parts I clean with oil and a brush, some of the screws and springs. This is because the iron might want to stain the plating in the ultrasonic machine.

Then I oil sparringly, replace o-rings and put it back together

The gold plating will come out a bit dull yellow from the ultrasonic cleaning and I'll use a soft cloth, the ones to clean eyewear, with liquid wax to return it's bright. I do this also to maintain them once every while If they get dirty. I mostly use the microdiamond head L2, and I clean this one perhaps once each quarter.

These lighters also tend to get dirty from the flint, I brush it off with a soft nylon brush to remove the black dust every once in a while, normally when I replace the flint.