OK, I'm in the market for a 300 series MB diesel, and several of the kind members here have said that a good way to tell if the engine is OK is to remove the oil filler cap and check for "blowby". Being new to diesels, I think I know this is unburned oil getting past the rings, but I'm not 100% sure what's normal and what's not. Exactly what is it that I should be looking and/or smelling for?

Robby