I just had the valve cover and half moon gasket of my 4d56 replaced yesterday due to oil leak. Only to find out the leak worsened when I got home.

I suspect that the mechanic used a wrong type of sealant (Pioneer black rtv silicone - Republic Chemical Industries Inc. - Pioneer Adhesives, Epoxies and Resins - Mighty Gasket ). If this is the culprit, whats a good gasket sealant?
Also, whats the proper way to install the gasket? Just a dab of sealant on the edges or put sealant on the entire edge/groove of the valve cover?

TIA.