I've been reading allot of articles and it seems like this is still a 50/50 mixed opinion issue. I've got a fresh oldsmobile 403 so oil leaks are not a concern for me as all of the seals are new. I'm wondering if i should use conventional or synthetic oil after the break in? If synthetic i planned to use MOBIL 1 full synthetic 10w-30, should i use the zinc additive with MOBIL 1 synthetic or does it have a sufficient amount of zinc in it already? I like synthetic oils because they claim to have higher levels of detergent, so in theory if ran from beginning to end of the engines life cycle it should run overall cleaner?