Thanks for all the input on Mobil 1. I think I will use to 10W-30 in my 99 E320. The dealers here in southern Arizona still insist that they use 10W-50 in all the cars because of the heat here. But they don't use synthetics. (Can you imagine what a dealer would charge for 9 quarts of Mobil 1? I can but it and take it to them for about the same as they charge for bulk conventional oil.) The dealers also seem to have this throwback mentality that dates back to the days of single weight oils (and I was there :-) that says you have to use 50-weight for hot weather. Both Mobil and MBNA assure me that a 5W-30 or 10W-30 will be good for any weather I find in most of the US. Mobil, in fact, says that the 10W-30 is more able to handle high temperatures than any conventional 10W40.
Trying to get info about what oils to use has been more difficult than I expected.