So.... which oil is the correct oil to use? (in a E300?)

I recently went to my dealer for some parts, and asked about oil. The parts guy says they (this dealer) no longer recommends 0W-40 for the E300. They are using 15W-50. I asked what about the 5W-40, and he shrugged and said 15W-50.

Of couse none of this makes me feel any better. I use 0W-40 is most of my other cars, so I put 0W-40 in my E300 (MY99). I personally don't want 50 weight anything around my garage after losing some camshafts in one of my old cars. (was using Castrol 20W-50 at the time)

I was planning on using 0W-40 untill the 5W-40 becomes available in my area. (eastern PA)