My Bug used to eat coils for lunch. Finally traced it to the combination of the steel braided cables I installed that were arcing, as well as the resistors were bad as well. The arcing would burn out the resistors to the point that I would have to keep a couple of spare coils and resistors whenever I went on a long trip...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car