Inverted forks oil change ? / 1992 KDX200SR

Hi there!

I've got a 1992 KDX200SR. I want to change the fork's oil since the bike tends to pull to a side (I've checked frame, wheels, wheel alignment, etc) and everything points to uneven oil levels on the forks.

Does any one know what kind of oil (viscosity) is better and how many ounces I need to put on each fork? It's got inverted forks.

Thanks a lot!