Hi guys, 

A friend of mine is looking for an excellent BMW E46 mech. Someone who understands the internals extremely well

The car has been checked many times and the the diagnostics machine keeps giving a clean bill of health. 

However, the car's performance and fuel efficiency is very bad. Online forums suggest checking VANOS seal leaks and/or engine compression ratios issues

Where can one get a mech/garage that can do this level of detailed check, not the usual spark plug, fuel filter replacements

Tony.