opti coat 2.0? I used it on my E-class, also black. Looks amazing and beads water like crazy. No rinse wash might be fine since he is buffing the car anyway, but why create more work for yourself (imo). 1 buffer pass may be fine depending on the level of swirls you have, if you use an automatic car wash or use a sponge to wash your car forget it.
2008 Mercedes-Benz CLS550 Iridium Silver/Black Leather -- P2/321/881 (leasetraded 1/10)
2002 BMW 325i --Topaz Blue/Natural Brown Leather --SP/PP/HK/CWP/Bi-xenon (Sold 9/06)