One of those heavy plastic ice scrapers that's had a sharp edge worked up on it can to some good and won't harm the metal.
Manual use of a safety edged razor can work too, but use no handle on it even if you've got one onnaconna the handle means extra leverage and that can lead to inadvertantly grousing the metal. If you can't work it by hand, then you don't need something to make things worse basically.
A metal putty knife with the edge sharpened but the corners rounded wouldn't be out of the question either.
Thanks, I ran out and bought a can today; very good results. I started with the nail polish remover and that seemed to be starting to work but I had to quit for the night. I resumed with the Permatex Gasket Remover, let it sit for 5 plus minutes and the gasket started to loosen up quicker than the polish remover.
It came off more in layers than chunks. I used a metal scraper with rounded edges (carefully), and cleaned up the residue as I went along. It really did not take too long. Use rubber gloves and decent ventilation.