I'm new here and i have a similar problem with my cap and rotor that i just can not seem to figure out. I work on a lot of vehicles and have done a lot of research trying to find out why my truck is destroying the inside of my cap and rotor but i am at a loss. I have replaced the distributor with and aftermarket aluminum one but for some reason it is still coming up with a corroded cap and rotor within a few months of putting a new one on. It happens in summer or in winter and the truck will still start. It starts hard and you can hear it most definitely has a miss and i've replace the coil and ICM module with brand new ones from chevy. I have been going through and checking that none of the grounds are broken and cleaning them (found all the ground locations in the factory manual). I have also noticed that one of the screw heads inside the new aluminum dist is completely rusted like it is getting moisture but I just have no clue how this could be happening. I also live in California which is definitely not a very wet or humid/cold state by any means. Any suggestions or help would be greatly appreciated.