I recently bought a 2nd hand bumper for my S3, to replace the knackered on that's on the car at the moment. Problem is that it's silver and my car is Ming Blue. I'm going to get the bumper sprayed (obviously) but to save a little on the cost, I was planning on prepping and priming it myself. What do I need to do to prep the bumper before applying primer? What primer should I use, and where do I get it from?