Lifting the car up for a while and letting the suspension hang unsupported may be affecting the oil and gas pockets in the struts. I am assuming, like other MB's the struts have a high pressure Nitrogen gas chamber to keep the oil in the strut pressurized so it does not cavitate when shock is working. Cavitation causes the shock damping characteristics to change to the point where the shock doesn't function as designed. How letting the unit hang and stretch out fixes this momentarily is not clear to me, and it would depend on the exact arrangement of the innards of the strut. But it seems likely there could be something here.
Anyway, ifvyour problem is shocks/struts and I think that is unusual at your mileage. So is a loose rear end or a problem with the differential question raised by the dealer service guy. The car should be under warranty at 50,000 miles, and if you bought it from a MB dealer it should have been Starmarked and have a warranty up to 100,000 miles. Struts normally don't go out quickly, but I did have one on my 190E 2.3-16 go in the first 5,000 miles so it is not unheard of, and should be a warranty item.
Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)