I have had a BMC 1.5 engine now for 19 years and since it was installed by AMC Diesels I have always seviced it as recommended by the installer, ie, change the oil and oil filter every 175 engine hours and the diesel filter every 350 hours. I have done this for the past 19 years and the engine has never let me down. Still had to have the usual problems seen too, like cylinder head gasket, fuel lift pump leaks etc, but it has never missed a beat whilst cruising. Also told to only use engine oil with a CC rating. The engine hours are now approaching 11,000 since it was installed.