Classic symptoms of loss of gas from tailgate struts. Always shows up at low temperatures first. Best fix is to replace both of them. It is a bit fidly to do but worth the effort. I did this job on my '90 300TE last year.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Yep, just replace both of them.

I believe I wrote-up the procedure, but if you're not comfortable have someone who's done it MANY times, do the install.

If done correctly, you don't have to remove the entire rear-hatch (do one side at a time).

Also, use ONLY Mercedes OE parts, not OEM parts (e.g., FEBI/Bilstein).

I tried OEM, and had to replace them 2-years later.

:-) neil
1988 E36T AMG
1993 500E