Bigddiesel

So it started with oil dripping on cats and smoking. Had the cam cover gaskets changed when I did the timing belt. They also told me I needed output shaft seal it was leaking. Did that a few months later thinking that would solve the problem. Still have a burning smell brought it back to the indie shop to have them take a look. They washed down the engine with a dye and found nothing. There's no smokie of any kind or drips under my car. Engine bay is spotless. Can't figure it out