Hi, I'm a newbie when it comes to removing rust, so I would really appreciate anyone's help. The hood of my "new" 66' convertbile has rust all over it. When I began sanding it, I get to the shiney metal in some parts, while other areas remain a darker grey. When I look closely, I see the darker areas appear to have tiny pinholes with rust imbedded in them. I am afraid to keep pushing on the sander and digging deeper. Does anyone have suggestions on how to proceed? Thanks.