Just to second the last post. My 560SL was new to me a year ago; at the first oil change, the shop used 10W30, which resulted in smoke taking off from rest and consumption around a quart per 500 or less. Switched to 20W50 high-mileage-engine formula Valvoline, with no more smoke and consumption less than a quart per 1000--more like 1500 as I recall.
I made the switch after noticing the manual calls for oil on the order of what I used--15W40 at least--for temps typical of summer here in Michigan. RTFM still works....
