I still think that you should investigate this from a misfiring angle.
Make sure that your ignition components are in good shape.
Put a fresh set of plugs in.
Spray some carb cleaner around the intake manifold and injectors and see if you can find a vacuum leak.
See if you can isolate the miss by "cracking" the lines on the fuel distributor one-by-one. If you crack one and the miss does not change, then you have found it. Replace the injectors and seals on the weak cylinder(s).
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe