I have used Turner Service for the last six years both regular service and modifications like suspension and LSD. Prices seem fair and they know their stuff when it comes to mods.
They used to be the same as Turner Motorsport racing and know what works on the track.
https://turnerservice.com/
Turner's racing team trailers and race cars can be seen providing additional motivation and risk to your wallet
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[FONT="Arial"] M235i 6 speed, MGM. Wavetrac LSD with altered final drive ratio, MPE, MPK Airbox, side skirts, diffuser, Dinan springs, LCAs.