My 2000 323i had been frequently plagued with low coolant. I had taken it to my mechanic and he checked it a few times and said he couldn't see anything wrong. Well today his response was totally different. He had detected oil and coolant mixing and told me that I would need to replace the engine. He sort of irked by saying that you were careless with the oil changes as you have to have them done every 7-8K miles. I told him BMW recommends that this be done every 15K miles...his response was pretty rude that "then you better take this car to BMW dealership". My question....if I go for replacing the engine, what sort of a price tag am I looking at?