Mr. Bill, you're nuts
....Just kidding. But I don't understand why you'd want to write off your current well maintained and almost perfect car, with which you sound as though you are very satisfied, in favor of a one-year-newer unknown quantity with lower mileage (so far as you know) but a bad driveshaft and a leaky timing cover, and who knows what else. I know that folks are tired of hearing that the mileage isn't the fundamental concern with these cars, but I think that's largely true, with MBs and with other cars as well; a well maintained high mileage car will usually be less problematic than a low mileage car which has been abused.
I wouldn't even think of switching to the other Benz. The decision with respect to the Bimmer would depend on what you're looking for. If you're really looking to get into something with a little more go, then that would be understandable.
It's been a while since I owned a BMW, but my general recollection was that parts and service were usually more expensive. It was more common to see entire assemblies replaced at great cost, where items on a Benz might have been repaired. Nothing scientific here, just perception. Classic examples are small things like electronic antenna aerials and wiper blades, that can nickel and dime you to death with a Bimmer.
Good luck with your decision.