Old engine oil, HE! HE! HE!
Had a old 69 buick with a rope seal that liked to leak.
Everyone else's stuff was rusted out from salt on the roads in Michigan.
Shoot everything on that old buick was solid, after I fixed that old rope
seal it tried to rust so I pressure washed it and sprayed it down with rustoleum.
I cleaned all that off when I got to Florida and it was still rust free.
Kurt