I haven't tried a clay bar but as I said in other posts, Gel-gloss (purchased at home Depot or other hardware store) appears to do the same thing. I've used Gel-gloss for over 10 years on 6 different cars and it works great by hand or with a buffer for removing light to medium oxidation or light scratches. It's cheap and easy to use and works fine for clear coats.
2004 E60 530is, Delivered 12/12/03, TiSilver/LGrey, PP, SP,PS, PDC, ACC, FRS, Step, Xenons, clear bra, body colored rear inserts. (Retired, 1983 henna red 320is)
2004 Corvette Z06 Commemorative Edition