Here's a link to msn autos. It's the page that shows consumer reviews. You can see if the review is for an SL 320, SL 500, or SL 600.
There are fewer reviews of the SL 600's, but if you toggle through the different years, you'll get a good idea of what people like / dislike about the car. The engine is the same throughout all of the years, so it really doesn't matter about the year:
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".