Discovered John a few years ago when I called him up to diagnose a cracked cylinder. Have been using him exclusively ever since; for car services, to emergency calls. He arrives quickly, I got stuck at a servo today, car wouldn't start. Called up John and he arrived within 20 minutes and I was back on the road 5 minutes later.
John is thorough and walks you through exactly what the problem is and how he will fix it. Very reasonably priced too!
Cheers John!