At 40,000 miles I took the car to my BMW dealereship because the Check Engine light came on. The dealer found 14 of the 24 hydraulic tappets to be the fault and they were replaced under warranty. At 98,000 miles (with just 2,000 miles left on my extended warranty contract) the same thing happened. This time, however, along with all of the hydraulic tappets being replaced, the BMW dealer also had to replace the cylinder head due to defective threads in the cylinder head casting encountered upon reassembly of the engine. The repairs took nearly a month to complete - and would have cost $4,000. if not for the warranty coverage.