repeatedly defective ignition cassette

Hello, my 9000 2.0t (150 hp) Bj 1997, 133,000 km, suddenly no longer started 14 days ago: Ignition cassette defective (roughly burned). New part built in, ran wonderfully. After about 60 km again jerking while accelerating, always worse, hardly ran, until the engine completely went out. ADAC measured: When starting at the ignition cassette no rashes of the measuring instrument seen, smelled also probably a little burned. So: again ignition cassette! How can a new ignition cassette after 60 km defek again The ADAC man said: Saab never breaks (can I operate after 20 years), but the ignition cassettes are a known weak point. Is he right? Thanks for a helpful tip! Jens Baum