Leaking valve cover gaskets but no oil

[millertime1234]

Hey guys I had a quick question for you, so i just replaced the vapor canister and valve as instructed by a diagnoses from a local shop however they also proceeded to say my valve cover gaskets needed to be replaced due to a bad leak. Now I thought about this and took a look at my valve covers(from what I can see without moving anything yet) and didn't see any signs of oil leakage at all. Is it possible to have bad/broken gaskets without any oil leakage?
Thanks!!

 

[boominXplorer]

They leak at the back corners the worst and where you can't see. The leak will come down the back of the engine and run over everything which you wont see from the top. When they get bad enough it will make it down to the exhaust and smoke.