For a 1990 I really like synthetic motor oil like mobil1. In the winter, I would use 10w-30. in the summer 10w-40 or even 15w-50 if you have over 100k on the engine. You have to use a special and expensive fluid for the power steering. The part number is 000 989 88 03. You will have to go to a good import part store for this, it is made by Bilstein. That is what the factory recommends.