A technician came out today and determined that the problem was moisture in the air line. There is no dryer/filter between the compressor and the plasma cutter. The moisture in the system caused the start cartridge to erode because of what he called double arcing. There is a water trap of sorts on the plasma cutter but it is largely ineffective.
I haven't been able to test the results yet. I still have to install a water trap/filter/dryer, whatever they are and then test it.
Hopefully this information might help someone else.