First, the machine next to it in the photo IS a Groetchen 'Club' Deluxe and you can see it in action at this pennymachines link: https://pennymachines.co.uk/Forum/vi ... =16&t=2621
As to the painting, I don't do anything special at all really. Usually I remove all the old paint with Nitromores paint remover, although this Hi-Top's old finish was so good I just sanded down the few chips until they blended in. Then I spray with a can of metal primer (white). I find the Plasticote one is very good, then I spray with Hammerite smooth paint. In the case of the Hi-Top, I used Humbrol spray because I wanted that particular yellow. The real key is loads of very thin coats about 20mins apart. The first few are very unrewarding because they don't cover the primer and you feel you want to spray a thicker coat. Don't.
The masking tape you use is more important than you might think. Cheap ones do not stick well and do not release cleanly. The best is the green tape you can see in the photo. It's called frog tape and you can get it in Homebase. For sure, it's expensive but pulls away clean and sticks firm.
Sometimes I strip the machine right down to the basic parts for painting (see my post 'Bonanza Star re-born') but it isn't always needed if you mask correctly. The Hi-Top in the photo has all the metal work and glass removed but is still attached to the case and the jackpot unit is still fitted. Only other tricks I can think of are, use a spray can grip (available from Hobbycraft
) and don't drink more than two pints before painting the coach lines.