Frodo
If section #16 is leaking at the O-ring or anyplace along the length of the oil fill pipe you will see a slight oily residue. The oily residue will cause the road dust and dirt to stick to the engine. If there is no oily residue you can blow the dust and dirt off with an air hose. So just by blowing you engine off you can tell if you have any leaks or not.
If you have any oily residue you most certainly have vacuum leaks as well.
Threaded Mode
