Well, we'll probably get a flurry of opinions on this one.
MY opinion on a 104 engine like yours, is to stick with non-synthetic. Synthetic has it's advantages, I'm not knocking it. It is pricey, however, and I feel the benefits don't justify the cost. ESPECIALLY if you plan on using the same change interval as you would with non-synthetic (say 3000 to 5000 miles). MB of course just mandated synthetic oil for 2000 on up cars, where the services are paid for while the car is under warranty, so the synthetic now has the German guys in the white lab coats standing behind it. BUT, the cars are under the FSS system, these cars are going upwards of 10000 miles without a change, but if you realize it's 8 1/2 quarts of synthetic oil, it all seems feasable to me. In that case, I say go for synthetic, 'specially since MB is footing the bill. But yeah, if it were mine (in your case) I'd go for the non-synthetic. I'd recommend Penzoil 10W40 in the summer, and if it gets really COLD in the winter, use 10W-30 in the winter. Here in Wisconsin in the winter I'd use 5W-30. We were running bulk 10W-40 year round up here several years with no oil-related cold weather problems, so the 10W-40 I believe would probably work well for you year-round actually. And don't listen to this BS about "Penzoil being PARAFIN based oil" and all that hoo-ha. It's good stuff. There has been a rash of 112 engine problems all being blamed on FSS, going too long on oil changes, etc (which actually may be why MB now mandates the Mobil1 oil). There are 2 dealerships in our district that aren't having problems with the 112 engine, the one I work at and one other. What do we have in common? We were both using Penzoil 10W-40.......so take that all you Penzoil-parafin poopers. Let the oil debates rage.......