I’d go with WD40 on metal parts and a clay bar then polish on painted surfaces. That’s what I do the car with.
The roads up here tend to get "top dressed" regularly. The roads dept sprays them with tar then spreads a thin layer of fine gravchips over it and rolls them in. The excess is supposed to get swept up but there can be loose gravel around for weeks, and after it has been recently done tarry chips and spots of tar can fly up leaving tarry deposits on the paintwork which may have been the case with the OP. Some of the worst roads I have been on are on Skye. The main road from Kyleakin though Broadford to Portree is fine. But beyond that they are mainly a collection of holes that have been filled in then top dressed over the top. Leaving a series of near invisible bumps. Guaranteed to test any suspension.
