So on Rock Auto this morning for a 1996 SL320 lift support they have various ones listed:

1) FEBI 27742 at 272 mm long.
2) AMS 4049 at 7.21" compressed, 10.71 extended.
3) FEBI 27734 at 242 mm long.
4) SCHS SG403031 at 7" compressed, 11" extended.

#2 & #4 above are listed as trunk lid parts. The other two don't say.

For a 1996 SLK230 and 2000 SLK320, they have:

Monroe Europe ML5680 at 365.5 mm long listed for the trunk lid.

My car is in the shop right now, so I can't measure the struts. It just seems like you ought to be able to use the length and spring pressure and find a suitable alternative.

Thomas