Just to pile on on the mileage vs octane question: My Saab, per the manual, will run on regular with less power but premium is recommended. Tracking the car shows that premium produces over 10% better mileage, usually 11-12%, and the price difference these days is more like 5-6%; it's consistently cheaper per mile to use premium. I haven't tried it in the 560 cuz that's an old enough engine I don't trust the ignition system to be that sensitive, and the manual says use only premium, but for a car of the vintage of the original poster I strongly suspect the Saab experience should be instructive.

__________________
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)