I have a 2008 ML 320 CDI with continental 107H's. 255 50 19. I have 20,000 miles on the car and needed to replace one tire last week after the sidewall got damaged. I have read alot about the repercussions on having tires with different wear patterns and sidewall height (even if they are the same make and model) on an AWD vehicle. I am not really sure if i should replace the other three tires or leave it the way it is. the tire place i went to said the other three tires have around 15000 miles left on them. any thoughts/suggestions? Thanks.