Bull @!*% to the spark plugs cracking on their own. When you were over tightening em or taking em out you prolly cracked them because of a ****** $1.59 spark plug socket. Nothing wrong with bosch plugs, why do bmw, mercedes, fiat, volvo, and 90% of all european companies run those? Hell, the factory bmw race team run bosch silvers or coppers in the m3's. The bosch platinums are @!*% to use on old cars, dont use them. They were meant to be run on modern engines with modern ignition systems such as coil on plug or distributor-less. If you are having running problems with them, i bet you have a flaw in your ignition or fuel system. This comes from a guy who has been a professional auto tech since i was basically born. I also road race, auto cross, and do the occasional road rally.