you replaced the cap and rotor with new parts, or just cleaned and replaced the old ones? Had an identical problem on my '94 SL 500, first cleaned up the old ones, still had the problem, replaced with new, problem solved.

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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000