Of course there is a difference in the shocks. Just look at shocks for a wagon, they are $200+ a piece. On cars with self leveling systems, there is a hyd. line that goes to the top of each rear shock. What do you think the hydraulic fluid is for? The accumulators (nitrogen cells) are what pressurize the hydraulic fluid that goes to each shock to raise and lower it.

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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