Bosch Platinum plugs

The pick up coil was probably the culprit right from the start, and not the plugs.
AC's use to crack the porcelain and would slide down and cover the electrode. Take them out and look at them and it was fine. Then you turn them over and find the problem.
The NGK U groove are just relabeled Nippondenso plugs. They work well. I never had a problem with the Bosch Platinum, But if I recall, they were designed for a hotter spark (HEI system, or better coil).