I replaced the spark plugs since there were oil on spark plugs and I replaced the valve cover a week ago. while I pulled out the spark plugs, I took pictures of old spark plugs and inside and I still see some oils inside of valve cover even if I replaced it and cleaned around gasket area before. do you have any ideas?

I just pulled out new spark plugs if there are oil on them but yeah new one also have oil on them... what's wrong with them..? probably there were some oil leaked into deep before and remained?

anybody can help?

Yes I did

Yes I do see sometime when rev at idle (only when it's warm)

I believe it was blue smoke.. it's pretty random to tell you when but It only happened when I rev after I drove around. I don't see it every time tho.

Suggest a compression & leak down test.