Oh Boy, the first oil thread for 2005?! Hope its a short-lived thread
Well, I'll stick my neck out and tell you what I do, for my gasser. I use RedLine 10W40 (synthetic) and change it at one year intervals, I only put 3000 miles on it a year, maybe more or less depending on if one of the diesels is out of commission for some reason, like one is now getting repainted after vandals jumped up on the hood and it was bent up nicely (thank you, Mr. Vandal, now I have new paint to match the four fenders and doors that were keyed a few years ago. The shop is also repainting the trunk lid with the same mix so the car has effectively been repainted 80% by two $100 deductibles, except for the top which doesn't really need it yet).
Letting a car sit for many months without running the engine is bad.
I do run the gasser regularly, like today - its raining and I'd rather chance a wreck in that car (W115) than the 123 or 124 diesels. Handles better too BTW.
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 296650
1983 300D 243280
1985 300TD 223470
1987 300D 262300