It is well know that if you inject a water base the depot is there in 4-8 hours. This is because the body is made of water and knows exactly how to remove the water.That is what the body does as part of metabolism....remove water. Oil is a little different in that it takes the body longer.This make take 12-24 hours. Now what if we made gear in motor oil?
The whole thing would be removed and you would get no test. Since the body cannot assimlate,use, or breakdown motor oil then the whole thing is gone.