On my coach it was there since new, but I never get any oil coming out of it. I do not know which engine you have because I have read both Cummins and Caterpillar if over filled with too much oil will throw the oil out the breather tube. I have the 3126-E and have never had any problems like some have had. I put 19 quarts of oil when I change the oil. Originally this engine called for 22 quarts, but later on when lot of people were having the radiator problem and the breather tube had not been extended a revision was put out by Cat that the engine only required 19 quarts.
Now I am not sure about Cummins engines if you have one.