valve cover leaking oil & engine runs a bit rough at times

I own an entry-level Craftsman mower with the 550e Silver Series engine. Recently, the valve cover began to leak oil. I have tightened the three bolts holding the cover on, but it is still leaking ever so slightly. I do not believe these engines have a valve cover gasket...... and am wondering if using a gasket maker (such as permatex) would solve this problem.

My only other trouble with this engine is that it has had a slight surging/hesitation problem, but I solved it (for the most part) by buying fresh gas and using a fuel stabilizer. Even with fresh gas the engine isn't quite as smooth running as my old L-head Briggs. I think part of problem is the ethanol that is found in gas these days degrades quickly over time. I'm not sure if I should use an additional additive to help the engine run as smooth as possible (besides fresh gas and a fuel stabilizer). Any advice is appreciated.

I have had the mower for almost one year and haven't had any other issues besides these two problems. This is my first ohv briggs engine....... I like the simplicity of the older L-head models better than the new design. Perhaps the change in design is due to epa requirements.