85 wagon sls suspension works but one shock shot
 

I've been very happy with the SLS suspension in my wagon for years but it seems my right rear shock is starting to have issues.System functions fine in terms of self leveling but there is a solid thumping now whenever my right rear goes over any kind of bump or hole in the road.Almost sounds like the passenger rear door is being shut repeatedly(its that solid sounding a noise)
Car has no sagging issues and has new-ish accumulators.
Im thinking its a blown shock but if the leveling system is working?. . .
would like to repair but not sure whats going on.
Thanks,
Sam K
73'bmw 2002
85 300td wagon