The matt black covers will paint fine if they are correctly prepared. As others say above the secret is preparation.
Plastics need to be chemically clean - you must remove grease, wax, and polish before sanding the items so that the paint sticks. This is done with liquid preparation products.
The item must then be thoroughly sanded. We would use a 180grit wet n dry.
The items are then painted with adhesion promoter which is left to soak into the plastic for about half an hour (some products vary), then plastic primer and colour coat.
All paint must have a flexible additive added into the paint.
If you miss any stage the paint is likely to peel - nothing to do with the original covers only the preparation and products used. This is a better preparation procedure than BMW use and will ensure that the mirrors last for ages.
Whilst we use professional bodyshop products - everything you need is available at your local accessory shop and modern aerosols spray very well indeed.
