I need help with this for the upcoming Concours. The inlet on my V6 W210 is magnificently formed in an alloy and nicely in view, EXCEPT that it has an intricate surface finish that looks blotchy and seems to hold the dirt rather tightly.
Having tried cleaning it normally without much effect, I then tried (very lightly) sanding with 400 Wet & Dry which cleaned it up fairly well without going too far but the ingrained dirt is still there. I then tried turps, which helper a little but still...