Oily? Try washing up liquid or non-scrubby swarfega. This will obviously remove any polish or wax too, so I'd give it a quick polish afterwards.
I've also used Autoglym tar remover, not very good on tar but pretty good on oily marks.

I'm certain a clay bar would work well, but give fairy liquid a try first

(I used meths on my old van once, cleaned the area really well and didn't damage the paint... but it might yours!)