A lot depends on the type of fabric. I'm not sure when Ford started using vinyl as many older fords had a faux leather material that is thin and about the same as book cloth. I'm not as well versed on the mid 50s cars but the crown vic was a very upscale car in the Ford line so it would have been an upscale material for the time frame. If it's perforated then that complicates things but I don't know what it has. If it has cloth then depending on condition, it may be too frail to get aggressive with it. Something like a Bissel spot stain remover may work. I would try to contact a professional in the field of furniture cleaning to see if they could help. They would likely decline to work on a frail piece of material due to liability but if there is a way, they would likely know.