Water and a soft cloth. Still looks like new. Although I am starting to get some deterioration on the turbo heat shield. If anyone has ideas for making that look new, I would love to hear it.
Some of the tape started getting hard and peeling. I found this stuff on Amazon. It looks identical to the tape used on the engine wiring.
Amazon.com: Tesa Black High Heat Wire Loom Harness Tape Used By Mercedes BMW VW Audi: Home Improvement