check the warranty period, older ones has 2 (!) years warranty
it has since been extended to 5 years, but i can't recall when the change happened
new BMW usually has some form of service/maintenance package baked into the purchase. when the warranty was 2 years, it was for 2 years.
Now it should be 5 years
do check if the unit that you are checking out has the 2 or 5 year warranty