I am considering purchasing a GL350. I currently own a GL450. I'm curious as to what the major differences are in maintenance procedures/costs between the two. For instance, does the 350 require a different type of oil? How about the maintenance frequencies? What is "adblue" (sp?)? How do the 350 owners like/dislike the runflat tires? I personally don't like the idea of them. I've never owned a diesel before but I do like what reading about the MPG. Thanks in advance!