Maybe I need to clarify. I have sanded past that 5/8" that was under
the molding onto the finished floor so that the finish has been taken
off the finished area. Applying polyurethane on that area that had the
finish taken off resulted in a completely seamless transition. You
could not tell that anything had been done to the floor. The problem is
the area underneath the molding that is still ever so slightly higher
and darker than the rest of the flooring and needs to be brought down.
I am confident that if I can just do a better job on sanding that 5/8"
it will look much better. So about the belt sander idea...