Hi Nic,
For plastics look here for perspiration inspiration LINKY 2 issues, use build up primer to cover any scratches and use the correct paint for plastics or it will come off like cornflakes.
For a swing arm, Airhead is right. Tthere is no need to take all the paint off. I did this once and it took forever and made so much mess that I got really P'eed off with it. What you need todo is degrease, smooth down paint especially where there are ridges caused where the paint has flaked off and then spray. PJ1 if you can get hold of it otherwise Hammerite smooth is good.