I just read this about acetone and polyurethane... I will certainly try it on the heel though before proceeding.
Can You Strip a Hardwood Floor With Acetone?
By Chris Deziel, eHow Contributor
Floor installers in the past often used shellac or varnish as a finish. You can soften them by moistening them with a solvent like acetone, and strip them when they are soft, but doing so isn't the best way to do the job. Most contemporary floor installers use polyurethane instead of shellac. It hardens by curing and produces a much more durable coating, but because it cures, you can't soften it again by using acetone.
Shellac, Varnish and Polyurethane
Shellac is a natural polymer originally derived from a resin secreted by lac bugs and dissolved in a solvent. Some varnishes are similar, consisting of a natural resin, usually pine sap, in a solvent. You can soften either of these with acetone. Polyurethane, although sometimes called a varnish, is a synthetic plastic. Although it too is borne in a solvent, which can be similar to the type that carry shellac or can simply be water, it undergoes a complex chemical reaction with the air as the solvent evaporates -- a process called curing. The reaction is irreversible, and polyurethane doesn't become soft again.
Stripping a Floor With Acetone
Although you can strip a floor with acetone if it is finished with shellac or a similar material, like lacquer, most modern floor finishers don't use either of these materials as a final finish because they aren't hard enough. Acetone will soften some varnishes that were in common use before polyurethane became popular, making them marginally easier to scrape off, but the process is messy and time consuming. Even removing shellac or lacquer, which dissolve readily in acetone, is messy and labor intensive. It requires several applications of the solvent to do the job properly.