The old standard, automotive cleaning solvent, is call Stoddard solvent. It's available at any petroleum supply company.
PSC 1000 solvent, is probably Stoddard solvent, with it's higher flash point. Stoddard works well but, the fumes can get to you if you use it where there no air current or if you use a air gun to spray it. I had to breath a lot of it, when I was a mechanic. Not good. Also, with extended use, it effects your skin. It will make your skin tingle and itch. Prolonged use, will result in your skin peeling, too. So, rubber gloves would be good.
What I use now, is a industrial, water soluble cleaner. to be mixed 10/1, as max strength but, I use it straight, like carb cleaner. It will take off 40 year old slug and leave a clean surface but, doesn't remove the paint like carb cleaner and is very safe to use. I buy it for $22 per 5 gal or $5 per gal. I got 1 gal first to try it out. It worked so well, I went back and got the 5 gal bucket.