Getting to what you stated about the cat converter not being able to digest the zinc in the oil that was used in the V6's era - we can also include leaded gas - both plug up cats - lead and zinc are very close to being one of the same - look at babbit bearing material that was used - different ratios of both in different applications of engine usage. Zinc and lead are both excellent as a wear surface additives in oil - bearings surfaces and the bearing journals are cushioned by your oil.
NOT HERE