my 2001 astra estate is misfiring, been into the garage for a diagnostic and they have replaced the crank sensor but still misfiring once warmed up , I changed the plugs and air filter before it went to the garage . some people have suggested an engine oil flush but I have read this can damage the engine . had the car 3 years and do about 10000 k a year , I change the oil and filter every year and its due to be redone was considering an engine oil flush , but worried about damaging the engine , also gonna change the leads . any advice much appreciated .