What fluids should i really use,not what chiltons manual or parts store says?

What is your question?

I have never been able to find "SN" sae 5W30 oil for my 1997 4.5L landcruiser. I worry that perhaps there are additives in this "SN" oil that maybe lacking in the local parts store offers/carries. I can only find SJ, SL, etc. My question asks what oils/fluids should i really be using or are what im using suffient. What should i be using for my engine oil/where to get that? What fluid/oil do i use in my transfer case? Where do i get those? What gear oil/fluid do i use in my differentials? Where do i get those? Is synthetic better or required in said landcruiser?