First you may find a smart person tell you that the tappet cover is leaking. Then you tell your real mechanic you thing the tappet cover is leaking. Well the mechanic sees that the the PCV valve is leaking, so he replaces the PCV and tappet cover gasket and charges you for both. You pay the extra $90 dollars for an unnecessary tappet cover gasket, saying to yourself I knew it was the tappet cover gasket and everybody’s happy. But you still payed an extra $90.
Or, you tell them you think it’s the tappet cover, and a not so experienced mechanic takes a quick look and says “yup looks like you’re right” and quickly changes the gasket. Then in a week your back with oil still leaking.
It’s always good to be informed, but always tell your mechanic the symptoms only. The more detailed the symptoms the better.