I am an artist with a damaged area in my oil painting.  Can I sand the
damaged area (with sandpaper) and paint over the sanded area with new
oil paint, or does the new oil paint require a barrier layer? I am not
interested in acrylic paint information.  Thanks

there are some notes on technique here
http://www.noteaccess.com/MATERIALS/Pentimento.htm

Obviously the painting is dry, or you could not sand it. But very
little sanding is required. Simply painting over the area will adhere
to the dried paint. If a varnish has been applied, THAT needs to be
removed (using turp) before adding a new layer of paint.

BTW, did you know that many famous paintings were 'repainted' over
until the artist was satisfied? Mona Lisa and Guernica are a couple.