Hi, I found this site that may help:
Removing stains from an oak floor
Refinishing oak floors is just like refinishing oak furniture. You can
repair any type of imperfection without complete sanding (or
stripping) and refinishing. However, often floors are sanded and
refinished because this is the easiest route to a perfect new finish
or because the homeowners want to lighten the whole surface. You need
to decide whether repair or complete refinishing is in order for your
If there is a light or faded area, try rubbing the spot with furniture
refinisher on a steel wool pad. The strong solvent that will soften
the existing clear finish and spread around a mixture of softened
varnish and stain. This may even out the color variances. It might
also lighten the whole surface as the old, darkened varnish is
For dark stains, clean with a 50-50 solution of laundry bleach and
water. Stains that disappear quickly were just surface mildew. Any
remaining dark spots are water stains that have penetrated the wood.
To remove these, sand the area or bleach it with wood bleach. Wood
bleach is available at paint and hardware stores. It lightens the oak,
turning it almost white.
After bleaching, the grain of the wood will be raised and rough.
Smooth with sandpaper and then stain the area with an oil-based stain
to match the original color. Finally, seal with the finish of your
choice. I think wipe-on oil finishes are a good option for repairs.
You will need to be a bit of an artist with the stain color and final
finish to blend in the color and gloss. Always start with a stain
lighter than the final color you want to achieve. You can always add
more stain or a darker color stain, but it is difficult to remove a
dark stain color once it's in the wood grain. Also remember that the
clear finish will make the stain color appear darker and richer.
You can see why floors are often re-sanded to remove imperfections.
All stains, scratches, and damaged finish are removed with sanding,
leaving the surface flat, smooth and ready for a new stain and clear
finish. Sanding is the only way to ensure a like-new finish.