81 300td - strange behavior, rear suspension?

When I put the car in reverse, the tail end lifts up a few inches. When I put it in reverse, it sits down, almost like it's on the rear axle. Checked the differential mount this weekend, and it seems to be in good
shape.
However, the ride is really very smooth, especially through dips, where the car almost ignores them, even here in West Texas where we have some pretty crowned roads to channel our thunderstorms down the hills. Crossing one of these with any sort of speed in my Explorer and I'm airborn, but the MBZ takes it without much excitement at all.
I'd say it was my shocks, but putting my weight on any corner and then releasing results in a quick return to stability, no shaking. That's dips - little potholes in the road seem to rattle through the whole car. Not super bad, but enough to cause the jack to rattle in the back end.
I'm not sure what part the self-leveling suspension is supposed to play in all of this.
Any suggestions? Measuring the height of the rear bumper, it's the same in the morning as it was when I parked it 13 hours before, even over a weekend, so there doesn't appear to be a leak, no fluid on the driveway, etc...
I don't want to buy shocks, or even get into that mess without a good reason to do so.
Thanks for any input!
Tweaks
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From a Mercedes newbie. What is the difference between a 300SD and a 300TD ("TurboDiesel" I presume?) Did the TD replace the SD? Or is it another car altogther?
"300" is the engine size, I presume, in liters, right? A 300 is 3 liters?
"S" is apparently a body class And "D" I presume to mean diesel...
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In the USA: S means it is the large body. i.e. from 73 to 80 it was the 116, 81 to 91 it was the 126. T means it is a station wagon. i.e. in the 123, 124, and 210 body. D means diesel. T AFTER the D means Turbo. As an example: A 300TD would be a 78-79 123 body 3.0L non-turbo station wagon. A 300TDT would be a 1980 to 1985 123 body 3.0L turbo diesel station wagon. A 300TE is a gas engine wagon.

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This is normal, within a certain degree my 82 240D did the samething.. shift back and forth from reverse to neutral at the right pace and yoru car will appear to have hyrdraulics (although im not sure if its entirely healthy for the car, it never hurt my 240d).
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Thanks. It's just a relief to know I can now concentrate on some other repairs - this would have been a lot of bucks, pretty much any way I tried to go with it.
Tweaks
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MY 82 240D / 84 300SD / 82 300SD have all done this
guess in reverse its mating season
the case, minus a few cans!
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HAH! I wasn't going to go there...
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HAH! I wasn't going to go there...
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