Well with the w210 you have rust, stuck glow plugs, and being fairly slow compared to modern cars. I don't know much about the w211 V6 other than oil cooler leaks and that it costs $1800+ to have the transmission conductor plate replaced which can only be done at the dealer. The inline 6 w211 is definitely faster and handles better than the w210 by far, and still has the older transmission that is stronger and cheaper to maintain, but you still have the SBC brakes, black death issue, and to get a good one that won't have so many people lined up to buy it the seller won't bother letting someone get it inspected it will probably cost double what a w210 will too.