Crank case ventilation / oil smells

[Juular]

I'm not sure my crankcase breather is working properly, and I'm not even sure it is correct for the engine.

It's a '64 car but I've rebuilt the engine from a rusty bare block that was found in the car and using spares from a donor. It has an unvented oil filler cap, and an open breather that sticks out of the side of the block with a flame trap on it, which then goes down and out under the car. That's it.

I get a bit of an oil vapour smell when driving. I have also noticed that the bottom of the gearbox is covered in oil film. The film has a slight petrol smell so I'm thinking it's coming from engine rather than box. The engine oil level doesn't really drop at all, just completed a 900 mile journey and the level on the dipstick barely moved.

Where could the oil smell and the film be coming from? Would the wrong cap and breather cause pressurisation and therefore oil vapour to be pushed out from somewhere? Or is this all just a characteristic of an open breather?