Sometimes an oil leak may not be visible, yet can be very expensive to address. Case in point is my '09 Infiniti. I won't get into the specifics, but there is a paper gasket that can fail...if it does, it results in throwing a code...yes, a check engine light. Ultimately, it can result in the car going into "limp mode" necessitating a very expensive repair (in the neighborhood of $3K-$5K depending on who does it). At the very least, here in the metro ATL area...it would prevent you from passing the emissions test...again, costing a significant amount of $$$ to repair. It doesn't seem as though it's a very common problem, and so far (fingers crossed), I haven't had the issue. Some owners have reported that if they switched to a fully synthetic oil...the problem shows itself in pretty quick order.
The possibility of this issue has had me pondering if I should get rid of the car before it happens (that's if and when?). Ultimately, I decided to take the chance. I take excellent care of the car, and it sits in a climate controlled garage most of the time. Is it a gamble? Yep...but with the costs of cars these days, it's one I am going to take.