Reason(s)? All of the above.
I'm on my 3rd Benz diesel, and would like another. I like 'em.
Built like a tank.
Easy to work on
Built like a tank
Don't blend in with all the other stuff on the road
Built like a tank.
Comfortable.
Built like a tank.
Good fuel mileage
oh, and one more thing I like....built like a tank.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)