I'll try and make this short, I purchased my 2007 Mini Cooper S 2 years ago (62,000 miles now, 45,600 when purchased) and paid my local Mini dealer $800 to have the intake valves walnut blasted or so I thought (more on that later), the reason I had them cleaned was because of my misfiring and pre-ignition during low to moderate boost. Right after the intake valves were supposedly walnut blasted I still had problems with pre-ignition during low to moderate boost. So I did tons of research on Mini's with misfiring and pre-ignition here and everywhere, I found a product BG 44K Fuel System Cleaner, bought multiple cans and ran in each gas tank of either Shell V-Power 91 or Chevron 91 here in Southern California. I ran 15 cans in total every tank fill-up, I'm not joking because I noticed when I removed the plugs my pistons were going from black to aluminum gray, I could actually see the color of the aluminum alloy. Most of my pre-igntion during low to moderate boost began to go away as I used more cans of BG 44K, but when in Summers where the humidity was low (50% or lower) I started getting pre-ignition in moderate boost but no pre-ignition in very humid Summers (I know cooling effect high humidity). When I got my intake valves walnut blasted 2 years ago (15,000 miles ago) I asked the mechanic to take before and after pictures and I was very firm about it was asking, heads turned. He took before pictures (1st pic) and later when he was finished he stated he forgot to do the after picture. Hay before we start with looking at the pictures there's something you should know, my MCS consumes half a quart (1/2) of oil every 1000-1500 miles. Less consumption highway driving which is 75% percent of my driving. The first picture is the before picture the mechanic took of the worst cylinder #1 (left to right). His cameras screen was to small so he loaded it to the computer and I took a picture of the computer screen. I took these other four pictures two weekends ago, the second picture is the cylinder #1. They look like the same cylinder, I'm seeing the same picture just 15,000 miles later. The third picture is cylinder #2, forth picture is cylinder #3 and the fifth picture is cylinder #4. Looks like someone was using dentist tools. I don't know about you but it's my belief that cylinder #1 was never cleaned as well as cylinder #2, the last two were done in my opinion to a point. The last bit of that harder carbon I was talking about was not able to be removed with the shops walnut blasting tool. I'm interested in what you believe cause I think it was a half a** job at best by the Irvine Mini dealer 15,000 miles ago! No more Mini dealers ever!