Does the automatic transmission fluid in my 2009 BMW 318i saloon require changing at 100,000 miles, even though it purports to be a "lifetime" item? I'm looking to run the BMW for as long as possible and the transmission is working perfectly at present, but I'm concerned this will not continue to be the case if I neglect a vital service item. I'm aware the cost of the fluid and associated sump kit, before any labour charge, would be quite considerable.