THe owner's manual does give recommendations; it's included on the CD-ROM manual set I bought. If the budget doesn't extend to the new price, there's always Ebay...
I run 20W50 in mine in the warm season, which here in GR will hit the 90's occasionally; IIRC, 10W40 is ok for winter. I do recall that 10W30 is not to be used over 50F ambient; when it was misguidedly put into mine last summer, consumption went way up. I run Valvoline's high-mileage-formula dino and normally use maybe a quart per 1500-2000 miles, at 153K miles on the car.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)