Yes 10W is the correct oil unless it gets very hot where you live and its heavily loaded. We have an SL that I overhauled and use it on a water pump, had 15w 40 oil. It was hard to start, smoked gray and slobbered oil out the exhaust even after I took it back apart and rehoned the cylinder with new rings. I asked a question about that problem on an European engine web site and a responder rather gruffly asked why do you have 15w 40 oil in it when the manual clearly calls for 10W?? Thinking it would change nothing I changed it to 10W to prove the guy wrong,,,, guess what? oil slobbering, smoke and hard starting all cured.