Brabus has a perf. kit that includes custom camshafts, valve springs, platinum spark plugs, & carbon fiber air intake. They claim a 20hp and 11 lb.ft. increase over stock. They also claim that MB USA would still honor the 4/50 new car warranty & Flex Service, if the mod. is done by Brabus USA. Is this true ? Has anybody done any Brabus upgrade to their MLs ?