Some have used peanut oil, I have never used it, don't want the squirrels after my nuts lol..
I use armour all, but needs around three coats and re do regularly.
Only takes a few minutes.
I don't think my Terrano has ever been that clean. On the other side, mud hides the rust
As for blackening bumpers, I did mine with Motip Bumper Spray. 2 spray cans were enough for all the plastic trim.
The arches etc aren't black but a very dark grey:augie I use smooth peanut butter rub it on & let it soak in then buff off:thumbs some have found linseed oil to work great but back to black is total rubbish this days:augie
I bought a black plastic polish to keep the plastics on my quad bike in good condition.
Was a good few years back but I'm sure I have still got some left.
That worked a treat on the daughters faded ford ka bumpers.
Will see if I can find it and let you know what it's called.