Just as an update on the test-mule:

So far I've put ~150 miles on the car since swapping in the polished DV's. No nailing has appeared and I haven't had any problems with starting or rough running. Car is running the same as it was with the known-good DV's installed. Small datapoint obviously, but it does seem to indicate that DV polishing may be a useful solution for some of these persistent nailing issues.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]