To the previous post, are you talking motor oil? I hope not
Yes, there is specific oil called of all things, fork oil. There are several good brands out there, Bel-Ray, Maxima, Golden Spectro. Go by a local bike shop, they should all carry these. My B6 used exactly one quart for both legs. Also, you can mix weights. We used to do this on our old dirt bikes. ie: make a 12wt by mixing 10 & 15wt.