To be easy on the original part and finish I used WD-40 liquid from the square 1-gallon can from Lowe's and / or Kerosene for real tough greasy oily dirt, followed by WD-40, both with only soft brushes and rags. All to minimized the impact to the part and finish and paint marks, yet get it clean, and afterward a WD-40 wipe down 1 or twice a year after that to keep it looking fresh.