Well there are different ways to look at this probably. On the one hand 4 years is a pretty short amount of time to have any rust. I do recall that a TSB was issued for my C230 for a small area of rust at a weld seam at the base of the rear windshield. That is not exactly the same but similar. Mine never had that problem as far as I know though. I am superstitious about original paint as I can almost always tell when a panel has been repainted. Also my experience is that dealer body shops are often Maaco quality on a good day. Some are good and some not so good. This might be what the guy was trying to tell you. If it was me I might be inclined to get a bottle of touch up and some rust treatment and see what I could do, especially if it is very minor. You might end up with a better result than having the monkeys hit it with air sanders and god-knows-what. IMHO.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra