I just picked up a 98 e320 wagon 4 matic for my wife,to be safe over the winter...pretty cheap(4000$),been sitting in dealers lot for 8 months...and I am ready for SAT maintenance:bought 0w30 Mobil 1 from Wall mart on sale...(did not find 0w40),also brake pads,generic and I found the rear end all covered in grease,dry,no leaking,towards the driveshaft...what kind of oil gets in it,if it needs topping? 80w90?,thats about as far as I would go with maintenance till we get to know the car better...or it brakes down.Any difference between 0w30 and 0w40 on Mobil1?