Oil leaking from engine after valve cover was taken off to check for stuck liftl

What is your question?

New gasket and grommets were replaced after the mechanic said everything looked good and suggested an engine flush and oil and filter change. The engine was flushed and serviced. The rattle and ticking noise is gone...now there is oil leaking and burning on the exhaust manifold.a lot of smoke. I've asked the mechanic to fix the problem as there was no leaks coming from engine prior to him working on the vehicle. He has had my vehicle for 4 days now And he said he's checked and over looked everything. But it is still leaking. He said he is just going to silicone everything and see what happens.if that is going to take care of the problem. Please help with suggestions, advice?