Full tank of gas and empty trunk and rear seat. Go park on a very level surface (parking lot or some such place) and back up a good 50 feet or so and look at the car. Does it look like the rear is sagging as if you have a sack of concrete in the trunk? If so, stick a fork in the springs.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]