I always use an engine flush additive before each oil change. I used to have a Saab 900 and I flushed that at every oil change too, with no problems. Flush additive can cause problems if it is used in a very dirty engine, as it can loosen heavy deposits, large particles of which can block oilways. Some Saab engines, and for some reason particularly those fitted to the 9000 and 9/5, suffer from heavy silting - it is very common for the oil strainer on the pick up in the sump to become blocked and this can lead to engine seizure. I suspect that the best flush in the world can't dissolve the crud, and flushing just adds to the problem. Sad, but Saabs are disappearing very quickly indeed! They were a good left field choice, as is the Lexus.