As I have said before, diesels are very finicky about their timing. Even if a cylinder fires you can't be too far wrong, so best to leave it alone. Oil in the air intake (in small amounts) is quite normal, it comes from the engine via the cyclonic filter (that black plastic thingy on the side of the rocker cover). When you get the engine to go you could see how much blowby you get by removing the oil cap. If you can beg or borrow the equipment it would be a good idea to get a compression test done. Best via the glow plug holes. The compression should be if brand new 24bar, but most older engines are around 2. If you get 1.5 or less it is tickets and you would need at least a head job to get the valves to seal properly and, at least, to hone the bores and change the rings. What mileage does the engine have?