removing oil-like marks.stains when screening/finishing oak wood
I'm about to screen or lightly sand my old oak wood floors, but concerned about getting whatever substance (it looks like an oily substance - possibly from food or a bathroom product) - out in the process - before applying polyurethane. I've done a lot of wood furniture finishing and don't recall a way to get such marks or stains out (saw someone use a darker stain and work towards blending all - but that's not an option in this case).
I had the 60-yr old floors fully refinished 10 years ago when I first bought this house, as they looked so awful. All of the work (and cleaning thereafter) in the house since has removed most of the polyurethane and any seal (and of course, there are scratches, too).
I am also concerned that when my forced air heat 'blows'(given the season), that it will blow dust into my wet poly finish. Could that happen and is there a way to reliably protect against it?
THANK YOU for all information and advice which may help -