Contact a body shop supply company in your area.
They will have the products that you can use to properly repair and paint urethane rubber parts.Almost all cars these days utilize urethane rubber bumpers and body moldings .The paint system manufacturers and filler manufacturers make products expressly designed to be used in making cosmetic repairs to painted urethane rubber body parts.
The trick on the painting is that an additive has to be mixed with the paint that is to be sprayed on the urethane (Endura) parts so that it will flex ( be elastic) with the rubber when it moves.
If this is not done the paint will stress crack when the rubber part beneath it flexes.
The urethane if left exposed ,like in the cracked paint areas, weathers over time causing the paint cracks to develop into deeper fissures that extend below the surface of the urethane making it harder to repair.
Many body shops will skip over the paint additive step on low end work or maybe the paint system that was chosen will not work with the additive that will make the paint more flexible.