Failure #2 of MSD distributor cap on FE ???

[vettestr]

I have gone through way too many caps before learning why and how a simple check stops this failure. It kinda puts me in a funk with MSD and feel a simple note in instructions or in their catalog is needed.

Since I had junk caps sitting around I also drilled one out to check rotor phasing and was amazed how far off I found many rotor tabs too be. Most engines did run without cross spark or missing but ...geeez! You can not move the pick up enough to change much and swapping to another distrib. is the only cost effect fix (they do now sell a 2 piece unit $$$$). You can tweak the Vac. Advance plate to help a little.

The caps are drilled with a 1/8 vent hole to remove ionized gas/air but I am also seeing what looks like rust or a coating that covers the internals and especially the pick up wheel. Spraying everything with spray silicone and then wiping the wheel ends clean seems to reduce this but anybody know why or what is happening? I am seeing this in Arizona (its a dry heat ya know) so does not seem to be humidity related.... Any ideas guys, need your help on this one. I have drilled a second vent hole but no real affect seen.