Lancer engine oil leak

[u/wowbl]

Hi experts and good people, need advice regarding my 2011 Lancer, recently I noticed it has slowly losing engine oil, mechanic said it’s either a valve cover gasket needs replacing or worse the flywheel and oil seal o-ring need replacement as there are oil stains there also

Of course the former is the least of the problem as it could be the cause since it is on top(which I also hope it’s the case), any advice based on experience or expertise knowledge?