How to remove old, stuck-on protective foil?

[vavavroom]

How do I remove old, stuck-on protective plastic foil from an aluminum door sill plate without resorting to fingernail use? The foil has become hard and brittle and only comes off in small bits, the adhesive is also dry and tough. The adhesive can easily be removed with Goo Gone, the foil not so much. I'm not too crazy about using paint thinner in the area due to the proximity to plastic, painted areas, and the rubber door gasket. What's the safest chemical that will soften the old plastic foil so that it can be peeled more easily? The hair dryer did nothing.

 

[dwcopple]

Acetone on a towel and a hard plastic scraper

 

[RTexasF]

There are plastic razor blades for something like this. Tedious? You betcha but it will likely do the job.

 

[vavavroom]

I don't want to use acetone for the same reason I don't want to use paint thinner in this area. I suppose I could mask off the area to prevent damage to plastic, rubber, and paint. A plastic scraper might scratch the aluminum sill plate. I'm going to try my portable steamer with the smallest nozzle

 

[vavavroom]

The steamer worked. I used a piece of cardboard as a shield while I moved the nozzle along the door sill plate. The steam made the protective film wilt and release from the adhesive. I could peel the film easily off in a few big pieces and the remaining hardened adhesive came easily off with Goi Gone. Upon closer inspection I'm not sure if the sill plate isn't maybe stainless steel. In that case a plastic scraper would have been safe.