Obviously something is wrong, a set of tires a month sounds like a structural problem, and yes, don't throw a bunch of bucks at it.
I had a '97 and no problems until it was wrecked two years ago.
I would not think that hubs or lugs are the problem. Do you know a reliable independent with a good alignment set up? They should be able to diagnose the fault. I would consider the safety factor with what you describe.
Ed

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Ed
1960 220 SE Coupe (Ponton)
1999 E320 Wagon
2007 E350