The 4-matics are notoriously hard on tires, and MB recommends rotating front to back, or is it (back to front ;-)) every 3K miles. Since the tires are directional it would really be a lot of work to remove them from the wheels. My MB Dealer/shop will do a rotate & balance for me for about $65 (tax included) (which I'd have done at the 3K mile oil & filter change), but I thought I'd try to do it my-self to save the $$. If after rotating, the car feels like it wants to have the tires re-balanced, I'd have the rotate & balance done by the dealer/shop thereafter.
It would suck if the car needs to have it's tires re-balanced every 3K miles as the maintenance cost for doing this over 20K miles would just about equal the cost of the tires. In fact, it would be only slightly less to do the maintenance than to put the tires on, leave them on and replace them every 20K miles. So I'm hoping to not have to re-balance more than every 6K to 9K miles. Does anyone think this an unreasonable expectation?
As an aside, I bought the tires (Michelin Pilot XGT V4s, I think), at Discount tire where they did the initial mount and balance, and then took the car to the dealer/shop for a 4-wheel alignment. Afterward, the car developed a terrible shimmy at speeds over about 45mph. I took the car back to the tire store where they supposedly, rebalanced the tires, but made for little improvement. After that I took them to the dealer/shop where they re-did the balance job and all has been fine since.