1. Certainly will, they have used it for fence posts for years.

2. Whatever mix lets you brush it on, and have it soak in. Depends on how
much of the oil is sump oil and how much was petrol or kero from washing
parts in.

Sometimes fence posts are dipped in a drum of the old waste "oil" and left
to soak instead of brushing them. I dump all my waste oil and parts washer
waste together and it seems to work out pretty well to stop the termites
eating them, and I haven't had any of my posts rot yet, but I've had a few
burn.....

Hope this helps,
Peter