You just need to use primer on those areas for the paint to adhere.

lol

alexandro1290 paint sealer. Theres matte finish and gloss finish. I prefer the matte spray personally

The channel is dead dont bother

Most paints can get damaged to some extent. Usually, to help reduce this: 1) Sand whatever you're painting first 2) Use a paint primer for plastics 3) Lacquer paint for plastic is the most durable. Enamel and acrylic are less durable, but the next step helps this along. 4) Use a clear topcoat. The first 2 steps give more of a surface for your paint to grip into. Lacquer is the most durable paint. But it dries REALLY quickly. So it's strongly recommended that you use an airbrush for lacquer paint. Using a clear topcoat creates a protective layer over the paint. Now if you do all of these steps, be very careful around joints. Painting them makes them thicker. So it becomes more prone to paint rub and makes the joint a lot stiffer. Sanding it down before painting (this makes the joint looser before painting) will help with this. But you still have to be careful.