Their are a few product out that work (Eastwood products) but my experience with "diesel fuel" in a spray bottle has proven true for the past three resto's.
Take a bottle of diesel fuel and spray it on an area that needs removal. Soak it for a day or two and the coating will soften up and peel away like butter. Obviously the thicker it is the longer it will take. You will need to be patient and allow it to break down the coating. Others frown upon using it but it worked wonderful for me.
Please remember SAFETY at all times using any chemicals or fuel based solvent. Ventilate the area well, and always have a fire bottle or garden hose readily available. Also NEVER toss out solvent coated or likewise rags into the trash can. Fire can result when chemicals come into contact with other synthetic products. Lastly, alway's put out any open flames in your shop before using these products. Take no chances.
My uncle lost 8 prized street rods three years ago from a loose spark that came into contact with a oily rag that he forgot was on his bench, resulting in a total shop loss. He is still recovering from the loss of years of car collecting, and rod building. Insurance covered the loss but cannot replace his internal grief.
Wacky