I believe the "T" on the back of the wagons, stands for Touring. As in touring the countryside. It can gett maddening trying to figure this all out. I know that in Europe there are several different names for wagons. My VW Passat wagon is sometimes called a "Variant" over there. I have also seen Avant and Estate. If you go to the German VW web site they list my wagon as an estate and the sedan as a "limosine". BMW's wagon has a "T" on the it also. I am going forget about trying to sort out all the monikers over MB's 100+ years of building cars.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member