ok heres the skinny on smoke and tail pipes, rings/valves the smoke will come out blue in color always and the evidence will be on the spark plugs as black carbon coated..., head gasket the smoke will come out white as it burns the ethyl glycol and it will have a "sweet smell" to it the plugs will look like they have been "washed" as they have been with the coolant. as far as water in the oil my experience has been that if it is very bad you will see it, if it is just starting to go then you will not. the tell tale sign is the level on the dip stick is higher because the water has displaced the oil which is lighter in viscosity and will show higher on the stick when you shut the motor down meaning that the bottom of the oil pan has water in it and has pushed the oil up the stick. gas from the pump will make the oil thin and it will smell like gas. it seems like your gasket is just starting to go bad... my advice is to drain the oil out of the filter, and put some in a glass jar overnight this gives the liquid time to seperate if coolant, no seperation with gas but odor present, no changes in appearance with valves/rings.......
