[Turbod]

My BMW dealer said "lifetime fluid" is rated at 100,000 miles. My battery went out on my 335i six years after the build date. I would do your diff when you do the transmission. I would do your coolant when you replace the water pump and thermostat. Suspension is completely up to the driver. I would look to do the timing chain between 100,000 and 120,000. As for the belt system I have heard horror stories about the N55 eating the belt through the crank seal. I don't know if that is an issue for the N20 though. Most N55's are replacing them between 60,000 and 80,000 miles.