I went through the same thing with my '92 500SEL this past winter. You are going to have to replace the top strut bushing (or bump stop I think it is also refered to). The accumulators (spheres) that you replaced were the original culprits, but because of their failure the top bushings were damaged and all of the rubber is gone (hence the metal thump). More than likely only one is truly bad, but since they are not all that expensive I would recommend doing both. Good luck!

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold