The gray-white "ash deposits" you describe are totally normal and virtually unavoidable. Though unattractive, the ash residue does not interfere with secondary ignition function and, in fact, is beneficial to decreasing radio noise. Brass terminals are not quite as prone to ash accumulation as aluminum, but they still gradually burn. I think the ash accumulation predominantly is a result of ozone formation inside the cap exacerbated by the high discharge energies created by the newer electronic ignitions, which are necessary to ignite lean combustion mixtures across wide spark plug, cap and rotor gaps.
You can manage terminal erosion somewhat by smearing some silicone "dielectric grease" on each bare terminal protruding inside the cap, on the rotor tip and on the carbon button. As the dielectric grease burns, it will leave a conductive residue and help control ozone erosion of the terminals for improved cap and rotor life.
I use the MSD 8366 in combination with a very hot Crane digital CD ignition, e-core coil, and MSD wires sparking a 0.050" gap with 10.0:1 compression - and I enjoy good performance. My primary complaint with the MSD distributor is mandatory periodic replacement of the upper sealed ball bearing. Fortunately, the ball bearing is common and locally available from industrial supply houses, so occasional replacement is little more than a nuisance.
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