I think I know the kind of stain you are talking about. Long ago I experienced similar staining from Armor All and other water based dressings. Fortunately qd or a good wash always removed it for me. (black paint)
As for the Langka/Mothers, you may find it in a smaller auto parts store in the section where they sell automotive sand paper and body repair products( didn't see it in any big chain stores--Pep Boys, AutoZone, Advanced Auto near me)
PS
I see you are in Edison: here's where I saw the Mother's Langka, a place in Kendall Park
Car Parts of Kendall Park
3126 Route 27
732-821-7788
easy to get to from rt 1, go rt 1 south, turn at finnegans lane, make a left, stay straight, I think it's after 2 lights, its in a strip mall that includes the Kendall Park Post Office