Is the paint original or a respray?
If it's original, use a quality polish/compound for paint correction. I've had success with products from Griot's Garage and Chemical Guys.
If it's respray, and you know who did the work, go back to them and ask about their painting process (prep, paint manufacturer, etc.). They should be able to help you...
2004 is300 MSM
5 speed manual, LSD, Hotchkis TVS, Bilsteins, 18x8.5 +45 Konig Hypergram wheels, 235/40-18 Kumho Ecsta 720 tires, Leather/Alcantara.